PURPOSE:To send the result of self-diagnosis externally in addition to an output as a photoelectric switch through one output transistor(TR) by using a selection circuit so as to switch a detection circuit into a storage circuit while a voltage of a delay circuit restores to a prescribed voltage after power is interrupted tentatively and applied again. CONSTITUTION:When a control power Vcc is applied, a voltage of a capacitor 23 is still low, but one input terminal of an AND circuit 12 of a selection circuit 13 goes to a high level via an inverter 18, the result of diagnosis of a self- diagnosing circuit 8 stored in the storage circuit 12 is outputted from a TR 9 via an AND circuit 20 and an OR circuit 21. When the capacitor 23 is charged and the voltage reaches a prescribed value, an AND circuit 19 is opened and an output of a detection circuit 7 is fed to a base of the TR 9. Thus, the photoelectric switch enters the normal operation. When the control power Vcc is interrupted tentatively and applied again, while the capacitor 23 is charged, the result of diagnosis stored in the storage circuit 12 is outputted from the TR 9.