A photomultiplier tube including a photocathode, an electron multiplier, an electron collector, and a power lead, wherein the photocathode and the electron multiplier are disposed in a sealed transparent vacuum envelope, the electron collector and the power lead are connected with an external circuit outside the vacuum envelope, the photocathode is formed on the entire inner surface of the vacuum envelope, and the electron multiplier is located on the internal center of the vacuum envelope to receive photoelectrons from the photocathode in all directions for electrons multiplication. Because the effective photocathode area is increased, the detection efficiency of unit light-receiving area is improved.