Yamashita Hideo was born on May 2, 1899, and graduated from Electrical Engineering Department, School of Engineering of Tokyo Imperial University in 1923. In 1938, Yamashita was appointed Professor, School of Engineering of Tokyo Imperial University. Though his specialty was in Electric Machinery, he became strongly interested in statistical machines, consulted by a friend of his, Nakagawa Tomonaga who was working for the Bureau of Statistics, Japanese Government.

Nakagawa's problem was as follows: They had been using IBM punch-card machines for statistical computation. The needs for such computation were on sharp increase since late 1930s, but it became difficult, as 1940 entered, to import IBM machines, because the U.S. Government assumed them war materials. Would there be any way to cope with this situation Since they happened to know that Ono Katsuji, a mathematician, of Nagoya Imperial University had an idea for statistical machine based on binary arithmetic, Nakagawa, Yamashita, Ono, and Sato Ryosaku, a colleague of Yamashita's at the University, started to build an electrical machine for statistical computation with the use of electric relays as components. IBM punch-card machines require the input data to be in a form of a deck of cards, each of which was punched one by one in accordance with original slip of data. On the contrary, their machine accepts the data entered by many operators in parallel. Each operator has his/her keyboard, and the data entered is kept in a corresponding register consisting of relays until it is transferred one after another for accumulation to the counter of the display.

During the Second World War, the development was hampered by the shortage of components, and only a part of the machine was completed. It was in 1948 when they could complete the full machine with the use of 4,000 relays and 2,000 counters released from the military use. It was only 3 years after the war ended; Yamashita's group must have had to suffer from unbelievable inconveniences in promoting the development. A not-for-profit company, "Chuo-toukei-sha" established by Nakagawa and a Tate Minoru used the machine thus completed for statistical computation services as requested by Governmental Offices and Presses. This was the first computation service in Japan, though limited to statistical calculations. It was only in November 1956, 8 years later, when Yurin-denki-seiki launched general computation services with the use of relay computer, FACOM-128B.

This machine had 20 pairs of keyboards for data-input, and a dual arithmetic unit for statistical calculations. Pair of operators made input simultaneously through each keyboard, and the each set of data was temporarily stored in a register. They were compared with each other, and if found not identical, they are discarded, and the operators had to reenter them. The arithmetic unit was shared by 20 sets of inputs, and added them up one by one. The dual results of each addition were compared with each other, and if found not identical, they were discarded and the addition was automatically repeated. The sharing of the arithmetic unit did not give operators any feeling of waiting, because of the big difference of the speed between operators and electric relays. This machine was called "Statistical Machine of Yamashita Type," and, in 1951, NEC and Fujitsu sold each commercial version of it to the Bureau of Statistics, Japanese Government and Statistical Department of Metropolitan Government of Tokyo.

Yamashita became involved in the international aspects of computers in 1951. At the time, several universities and laboratories in the U.S. and Europe had developed computers, but for other Nations large-scale computers were considered extremely expensive. This situation led UNESCO to propose a plan to install a large-scale computer to be shared by all the Nations of the world. UNESCO invited interested Nations, including Japan that was still under occupation, to meet at Paris to get an agreement on the plan. The Japan Science Council discussed the matter, and decided to send Yamashita who was the leader of the research project in 1951 on "Electric Computer" supported by the Ministry of Education, as a technical adviser to Hagiwara Toru who represented Japan as appointed by Ministry of Foreign Affairs. The Paris Meeting decided to establish a Provisional International Computation Centre (PICC) in Rome, Italy, and Japan appointed Yamashita a Director of the Board of the PICC to represent itself. After the Paris Meeting Yamashita had opportunities to inspect computer installations in Europe and the U.S., probably as the first Japanese visiting them. Yamashita's report together with the news of PICC spurred the Ministry of Education to provide the University of Tokyo with a budget of ¥10M in 1952 to install a large-scale computer TAC (Tokyo Automatic Computer). Unfortunately, TAC took as many as seven years for its completion, but Yamashita had remained with the project in one way or another, and when it was finally completed in 1959, he was chairman of its administration committee.

In June 1959, UNESCO held the first International Conference on Information Processing in Paris, and Yamashita served as a member of its preparatory committee, because the original proposal for the conference had come up during the Board Meeting of the PICC. This UNESCO-supported Conference triggered the establishment of the International Federation for Information Processing (IFIP), and Yamashita together with Wada Hiroshi established Information Processing Society of Japan as a body to participate in the IFIP, representing Japan. Yamashita served as the first President of this Society.

In April 1959, Yamashita retired from the University of Tokyo, and was appointed Dean of the School of Engineering of Toyo University. He was conferred the Order of the Rising Sun, Gold and Silver Star, and awarded honorary memberships from Institute of Electrical Engineers of Japan, Information Processing Society of Japan, Japanese Society of Applied physics, and Institute of Electrical and Electronic Engineers. He was a member of the Japan Academy, Professor Emeritus of the University of Tokyo, and Professor Emeritus of Toyo University.

Yamashita died in May 27, 1993.