To provide a power supply circuit which is low in cost, is simple in structure, does not need a large occupation space, and can avoid a sudden interruption of a power supply which causes the inconvenience and to provide an image forming apparatus having the power supply circuit.

If a controller 4 decides that a sudden interruption of a power supply causes the inconvenience, a relay 2 is made to operate (turned on) and a circuit connected in parallel with a switching circuit is closed. If it is decided afterwards that the interruption of the power supply does not cause the inconvenience, the operation of the relay 2 is discontinued. During the operation (ON) period of the relay 2, even if a user of an apparatus turns off a switch 1, as the circuit connected in parallel with the switching circuit 1 is closed, the power supply is not cut off. With such a constitution, the power supply circuit which is low in cost, is simple in structure, does not need a large occupation space, and can avoid the sudden interruption of the power supply which causes the inconvenience and an image forming apparatus having the power supply circuit can be provided.