Photomultiplier

A photomultiplier comprising:

• a sealed container of which the inside is kept in a vacuum state;
• a photocathode, accommodated in said sealed container, for emitting photoelectrons to the inside of the sealed container in response to light having a predetermined wavelength;
• a dynode unit accommodated in said sealed container and including a plurality of stages of dynodes for emitting secondary electrons in response to the photoelectrons reached from said photocathode to cascade-multiply sequentially the secondary electrons;
• an anode, accommodated in said sealed container, for taking out the secondary electrons cascade-multiplied by said dynode unit as a signal;
• a pair of insulating support members for holding unitedly said dynode unit and said anode in a state of grasping said dynode unit and said anode;
• a focusing electrode arranged between said photocathode and said dynode unit, and having a through hole through which the photoelectrons from said photocathode pass, said focusing electrode for correcting an orbit of each photoelectron from said photocathode;
• and
• an accelerating electrode arranged between said focusing electrode and said dynode unit, and having a through hole through which the photoelectrons reached from said photocathode via said focusing electrode pass, said accelerating electrode for accelerating the photoelectrons reached from said photocathode via said focusing electrode,
• wherein said focusing electrode has one or more notched portions to be grasped by a part of each of said insulating support members when the focusing electrode itself is rotated around the tube axis of said sealed container.