PURPOSE: To obtain a focus signal in which a signal of a point of high contrast is not particularly emphasized by outputting an averaged signal of high frequency component in any part of a picture.

CONSTITUTION: When a video signal is supplied from a video camera 1, the video signal is differentiated by a differentiating circuit 2 and made to an absolute value by an absolute value circuit 3. This absolute value output is supplied to a maximum value holding circuit 5 through the first switching circuit 4. The circuit 5 maintains maximum value of the absolute value, and at the same time, reset to a reference level by a reset signal from a controlling circuit A. Output of the circuit 5 is given to an integrating circuit 7 through the second switching circuit 6, and the circuit 7 adds and integrates output of the circuit 5 in passing period of the circuit 6. The circuit 7 is returned to the reference level by a reset signal from a circuit A. By supplying integrated value of the circuit 7 to a microcomputer C through an A/D converter B, a signal for operation control can be obtained.