A brightness image is produced from a frame image input from a scope and a high brightness pixel group including pixels next to one another, of which the brightness values exceed a predetermined value, and of which the number exceeds a predetermined value, is detected. Only when the pixel group is detected, a microcomputer performs light amount adjustment. When no high brightness pixel group is detected any more, a brightness blurred image is produced from the brightness image. If the value of a pixel forming the brightness blurred image is greater than or equal to a predetermined value, the value is replaced with zero. If the value is less than or equal to a predetermined value, the value is replaced with a greater value as the value is smaller. Then, brightness conversion is performed on the brightness image by adding the brightness blurred image after replacement to the brightness image.