PURPOSE: To detect a focal point with wide field of view and high accuracy at high speed while simplifying configuration even when a detection frequency is set to a low frequency.

CONSTITUTION: A photographing optical system 11 forms the image of light flux guided from an object at an imaging device 13 for detecting the image of the photographing optical system 11. Then, the image is converted to an electric signal by a photoelectric transducer 15 while using a first-order optical system 12 and a second-order optical system 14 arranged near the position equivalent to the imaging device 13. A specified frequency band is detected from this electric signal by a frequency detector 16 and based on the frequency component signal of this frequency detector 16, the focal point is driven and detected by a peak detector 17. Based on the signal of the peak detector 17, the photographing optical system 11 is driven by a driving device 18.