PURPOSE: To attain automatic focusing by providing a changeover device outputting an output signal of a deciding circuit and a rectangular wave generating circuit through changeover and a motor driving circuit generating a driving signal of a motor with the output of the changeover device.

CONSTITUTION: When a focusing mechanism of a motor-driven lens 1 is driven by a motor 15 from inifinity to a point corresponding to he closest focusing distance and passes by a position corresponding to the position of an object, an output signal of the discriminator 10 changes from L to H level. Thus, the output of the changeover device 13 is changed over from the output of the rectangular wave generating circuit 14 to the output of the circuit 10 and the optimum focal point is passed by, then an output of an operating circuit 8 is decreased. Then the level is changed from H to L level in the circuit 10 and the motor 15 is driven again to infinity. Thus, the focal point of the lens 1 is placed at a point corresponding to the distance with the object at all times in this way.