PURPOSE: To improve the objectivity and the reproducibility of an optimum picture by detecting a maximum value of a detection value at an absolute value detection section in one picture by means of a maximum value detection section as sharpness.

CONSTITUTION: A video signal VDi obtained by a camera is converted into a digital signal by an A/D converter 1 to obtain a data as to the lightness for each picture element of a picture by using a sampling clock CK. The data is used to detect the absolute value of a difference between the lightness of adjacent picture elements by an absolute value detection section 2. Then the maximum value of the detected value by the detection section 2 in one picture is detected by a maximum value detection section 3 as the sharpness of the picture. Then the operator focuses the camera while observing the detected value displayed on a monitor television receiver. Thus, the objectivity and the reproducibility of an optimum picture are improved.