Oki began as a maker of telephone and telegraph equipment. They are mostly known for their printing systems, and at least in Japan for telephony equipment.

Several subsidiary companies have been spun off and merged again over the years.

The predecessor of Oki was founded 1881 as Meikosha Ltd. in Tokyo. The company was renamed to Oki Electric Works in 1889.

In 1924 they looked into radio production.

In 1954 there is a cooperation with the French CIT in the field of carrier telephones and telegraph equipment.

Around the 1960s Oki begins to produce computers. At the same time, consumer audio tape recorders are made.

According to "100 Year Step of OKI Electric Company" (translated by Hisashi Ohtsuka in his "Dawn of Tube Production in Japan", Section 006W,pages 1 and 2, the company developed and manufactured radio tubes from 1916 to 1919-1920. Research into vacuum tube development and production was part of the research carried out at the Tamachi factory in Tokyo. T. Baba was the manager of this department and was able to access "Electrician" and "Electrical World" magazines to help with this development. Tubes were made with nickel anodes and grids and had tungsten filaments. Problems with the old oil pressure vacuum pump meant that only "soft" tubes could be made because of low vacuums. By 1919 only a few had apparently been made successfully. The company began a "wireless equipment shop" in their Osaki factory and began making "hard" tubes. tubes were supplied for shipping equipment and broadcasters. The Tokyo Electric company took legal action for patent infringement and tube manufacture was discontinued.