A photomultiplier includes a photocathode and an electron multiplier. A typical structure of the electron multiplier is obtained such that a dynode unit constituted by stacking a plurality of dynode plates in the incident direction of photoelectrons, an anode plate, and an inverting dynode plate are stacked. The anode plate has electron through holes at a predetermined portion to cause secondary electrons emitted from the dynode unit to pass therethrough. Each electron through hole has a diameter on the inverting dynode plate side larger than that on the dynode unit side, thereby increasing the capture area of the secondary electrons orbit-inverted by the inverting dynode plate.