To provide a power failure detection circuit capable of solving the following problem: an emergency lamp goes out when a power supply is restored after power failure, by easily outputting a power failure detection signal suited to each rated input voltage for a plurality of different rated input voltages.

A series circuit of a transistor 17, which is switched on/off in response to heights of different rated input voltages of AC input voltage Vin and a resistor 16, are connected to a resistor 14 in parallel. An operation switching circuit 21 is provided, which switches on the transistor 17 according to the AC input voltage Vin in the case that the rated input voltage is high. The operation switching circuit 21 includes a holding means 21a which keeps the transistor 17 on during a definite period of time even if the AC input voltage Vin becomes zero when the transistor 17 is switched on in the case the rated input voltage is high. Furthermore, resistance values of respective voltage dividing resistor 13, 14 and a series resistance value of the transistor 17 and the resistor 16 are set so that the voltages at a middle point 15 are the same in the case of both the rated input voltage is high and low.