PURPOSE: To offer a photoelectric detecting device which does not raise a transient erroneous alarm due to the passage of an object, and is capable of raising an alarm in case an alarm is necessary even when the light is shielded by providing two storing circuits on a processing circuit which process the output from a comparator.

CONSTITUTION: When a photodetecting output exceeds the threshold level (operation level) of the first comparator 5, the comparator 5 sends out a high level signal ("H") to the output, also the second comparator 6 has the threshold level (safety level) whose level is higher than the threshold level of the comparator 5, and when there is a sufficient photodetecting output, the output attains to "H". Also, a Dtype flip-flop 12 being the first storing circuit, and a Dtype flipflop 13 being the second storing circuit are provided, the first storing circuit 12 is set by the rise of output signal of the comparator 5, the second storing circuit 13 is set under the condition that the first storing circuit 12 is set at the time of an "L" signal of the comparator 5, and both the two storing circuits are constituted so as to be reset by the "H" signal of the comparator 6.