A photomultiplier comprising: a sealed container of which the inside is kept in a vacuum state; a photocathode, placed in said sealed container, emitting photoelectrons to the inside of said sealed container in response to light having a predetermined wavelength; a dynode unit placed in said sealed container and including a plurality of stages of dynodes (DY1-DY8) emitting secondary electrons in response to the photoelectrons reached from said photocathode to cascade-multiply sequentially the secondary electrons, said plurality of stages of dynodes (DY1-DY8) being constituted by at least a first-stage dynode which the photoelectrons from said photocathode initially reach and a second-stage dynode receiving the secondary electrons outputted from said first-stage dynode in response to the reached photoelectrons; an anode, placed in said sealed container, taking out the secondary electrons cascade-multiplied by said dynode unit as a signal; a pair of insulating support members (410a, 410b) holding unitedly said dynode unit and said anode in a state grasping said dynode unit and said anode; and 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 correcting an orbit of each photoelectron emitted from said photocathode; further comprising: an accelerating electrode, for accelerating the photoelectrons reached from said photocathode via said focusing 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 being set to a potential higher than that of said first-stage dynode; and a structure for holding unitedly at least said accelerating electrode and said dynode unit in a state that at least said first-stage dynode and said second-stage dynode included in said dynode unit are directly opposite to said accelerating electrode. a sealed container of which the inside is kept in a vacuum state; a photocathode, placed in said sealed container, emitting photoelectrons to the inside of said sealed container in response to light having a predetermined wavelength; a dynode unit placed in said sealed container and including a plurality of stages of dynodes (DY1-DY8) emitting secondary electrons in response to the photoelectrons reached from said photocathode to cascade-multiply sequentially the secondary electrons, said plurality of stages of dynodes (DY1-DY8) being constituted by at least a first-stage dynode which the photoelectrons from said photocathode initially reach and a second-stage dynode receiving the secondary electrons outputted from said first-stage dynode in response to the reached photoelectrons; an anode, placed in said sealed container, taking out the secondary electrons cascade-multiplied by said dynode unit as a signal; a pair of insulating support members (410a, 410b) holding unitedly said dynode unit and said anode in a state grasping said dynode unit and said anode; and 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 correcting an orbit of each photoelectron emitted from said photocathode; further comprising: an accelerating electrode, for accelerating the photoelectrons reached from said photocathode via said focusing 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 being set to a potential higher than that of said first-stage dynode; and a structure for holding unitedly at least said accelerating electrode and said dynode unit in a state that at least said first-stage dynode and said second-stage dynode included in said dynode unit are directly opposite to said accelerating electrode. an accelerating electrode, for accelerating the photoelectrons reached from said photocathode via said focusing 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 being set to a potential higher than that of said first-stage dynode; and a structure for holding unitedly at least said accelerating electrode and said dynode unit in a state that at least said first-stage dynode and said second-stage dynode included in said dynode unit are directly opposite to said accelerating electrode.