To provide a detection system capable of reducing a commercial price by comparing whether or not laser light is radiated with a detectable range, and further, even when any other light than laser light is present, detecting the light with high accuracy.

In a detection system 1, a transmitter 3i irradiates a solar cell of a receiver 5 with laser light to which fluctuation has been given corresponding to a digital signal of a digital signal generating part. The receiver 5 receives light utilizing power generation by the solar cell in a solar cell power generator and further efficiently removes influences of disturbance utilizing a detection signal of an environmental light detecting part, in a differential part. Thus, an irradiation determining part can highly accurately determine whether or not the solar cell is irradiated with laser light. Moreover, in a data extracting part, processing for extracting digital data included in laser light, with which the solar cell is irradiated, can be implemented.