PURPOSE: To omit a wobbing mechanism and to reduce the weight of a device by arranging a liquid crystal lens whose focal length is variable in a lens to be used for an automatic focusing device, and changing the focal length on the basis of reference frequency.

CONSTITUTION: When the focus position of the focusing device is nearer than a focusing position, a reference frequency component is detected from a detecting output of a peak detecting circuit 42 by focus modulation based upon the reference frequency of image forming state on the photodetecting surface of an image pickup element which may be generated by the fine variation of reference frequency of the focal length by the liquid crystal lens 33 whose focal length is variable. When the detected component is synchronously detected by a synchronous detector 45 on the basis of reference frequency outputted from a reference frequency generating circuit 44, a positive polarity signal is obtained. The signal moves the focus position of the focusing device in the long-range direction. When the focus position if further than the focusing position, a reference frequency component having the reverse phase against said component is detected from the circuit 42 and a negative polarity signal is obtained by synchronous detection 45. Consequently, the focus position is moved in the short-range direction.