An inter-frame motion detector detects the presence or absence of motion between frames on the basis of judgment whether or not an inter-frame difference is not more than a set value. A vertical edge continuity detector calculates difference values between an object pixel and pixels above or below the object pixel in an inlaid picture, and detects whether or not there is horizontal continuity of an inter-field vertical edge on the basis of judgment whether or not the signs of the difference values are the same continuously over not less than a predetermined number of pixels, in the horizontal direction, including the object pixel. When it is detected that there is no motion between frames, and it is detected that there is horizontal continuity of the inter-field vertical edge, it is judged that a picture is in a completely still state.