PURPOSE: To obtain a photodetector wherein quatum efficiency and optical coupling tolerance are high, by forming a reflecting film for re-reflecting an incident light reflected by the element surface at the top part of a microlens.

CONSTITUTION: A signal light 17 which has entered a microlens 13 is reflected by a P side contact electrode, and approximately focused at the top of the microlens 13. The signal light is reflected by a Ti film 15 and an Au film 16, and finally once more reflected by the P side contact electrode. The signal light passes four times an N- InGaAs layer 3 which is turned into a depletion layer. When reflectivities of the Ti film 15, the Au film 16 and the P side contact electrode are increased, high quantum efficiency can be obtained while a light absorption layer is kept thin. Since the effective light receiving diameter is almost doubled by the effect of the microlens, except the region light-shielded by the Ti film 15 and the Au film 16, the decrease of optical coupling tolerance can be prevented when the junction diameter is made small in order to reduce the junction capacitance.