To provide a photoelectric cathode with which the number of emitted electrons can be increased.

This transmission type photoelectric cathode 10 comprises a semiconductor substrate having a first and a second through holes 10b, 10c neighboring each other. The shortest distance DL between the inner faces of the first and the second through holes 10b, 10c is set so as to make electrons (e), which are generated in the semiconductor substrate 5 corresponding to the applied electromagnetic waves XR and proceeding in the direction to the first and the second through holes 10b, 10c, escape to either of the first and the second through holes 10b, 10c.