Almost 90 years have passed since the invention of the thermionic electron valve in 1904 by Sir John Ambrose Fleming. During this period, the development of electron tubes created the so called "Electroni Age". Electron tubes played the leading role in the electronic equipments until the middle of the 1950s when solid state devices such as transistors and integrated circuits replaced electron tubes in various applications and accelerated the electronic age. This is a collection of data and memories about the research, development and production of electron tubes in Japan, contributed by some of the scientists and engineers engaged in their development.