Photocathode, electron tube, and method of assembling photocathode

A photocathode comprising:

• a light transparent member having a first surface incident with light with a predetermined wavelength, and a second surface opposing the first surface and emitting the light;
• a photocathode plate arranged at the second surface side of said light transparent member, said photocathode plate receiving the light passing through said light transparent member and emitting photoelectrons in response to incidence of light;
• a holding member attached to the second surface of said light transparent member and having a first opening portion in which said photocathode plate is disposed;
• and
• a supporting plate arranged so as to sandwich said photocathode plate together with the second surface of said light transparent member and having a second opening portion for exposing a part of said photocathode plate so as to allow the photoelectrons from said photocathode plate to pass therethrough,
• wherein said holding member has a fixing structure folded so as to be pressed against said supporting plate in order to press said supporting plate against said photocathode plate.