A photomultiplier which can be easily made compact has a dynode unit having a plurality of dynode plates (6) stacked in an electron incident direction in a vacuum container fabricated by a housing and a base member integrally formed with the housing. Each dynode plate is constituted by welding at least two plates (6a,6b) overlapping each other. The welding positions (W) do not overlap each other in the stacking direction of the dynode plates. With this structure, field discharge at the welding portions between the dynode plates can be prevented to reduce noise.