The moving image region detection device includes an updated block detection means, a natural image updated block determination means, and a moving image block extraction means. The updated block detection means compares pixel values between a frame of an input video and the previous frame, and detects a block including a pixel in which a value having been changed, as an updated block. The natural image updated block determination means calculates an index value representing a degree of continuity of changes in pixel values in the updated block, compares the calculated index value with a threshold, and determines whether it is an updated block of a natural image. The moving image block extraction means extracts a block determined to be an updated block of a natural image a given number of times or more in most recent frames including the frame, as a moving image block of a natural image.