PURPOSE: To prevent the unoperated state of a focus detecting circuit from being mistaken for the fault of a camera, by connecting a light source lighting control circuit to the focus detecting circuit.

CONSTITUTION: When a shutter release button is depressed, a switch S1 is turned on, and power is supplied to a light source controlling circuit LC, a focus detecting circuit AF, and a battery check circuit BC. When the output of a power source E1 is a prescribed value or more, the check circuit BC detects this state, and a magnet Mg1 is operated by the output of the focus detecting circuit AF to make the focusing operation possible. In this state, when the circuit AF is made unoperated, a light source B1 for focusing is not lit through transistors QB, QA, Q1, Q2, and Q3 of the circuit LC connected to the circuit AF, and thus, the unoperated state of the circuit AF is distinguished from the fault of the camera to discriminate the fault of the focus detecting circuit.