PURPOSE: To improve check precision and reliability by making a voltage boosting circuit inactive during the check on a power source voltage in the power supply circuit of a camera having the voltage boosting circuit.

CONSTITUTION: The power supply voltage VB of a battery E is boosted up to a voltage VL by a DC/DC converter, and the voltage VL is passed through a constant voltage circuit to supply a constant voltage VD to a sequence controller. While the DC/DC converter is in operation, a spike noise appears in the power supply voltage VB. When a battery check is made, the control signal DCC of the DC/DC converter of the sequence controller is decreased in level from H to L to stop the DC/DC converter temporarily, and a battery check signal BC outputted by a comparator COM is read and judged by the sequence controller while the source voltage VB contains no spike noise.