The interval designation section 222 sequentially alters and designates a movement interval D and a non-movement interval D′ in an entire interval. Each time a movement interval D is designated, the value determination section 223 determines the average value of the image variation amount array E in the movement interval D as a function value a of the unit rectangular function r[x] and the average value of the image variation amount array E in the non-movement intervals D′ as a function value b of the unit rectangular function r[x]. Each time a movement interval D is designated, a degree of divergence J between the function values a, b and the image variation amount array E is calculated by the divergence calculation section 224. Then, only the frame images contained in the movement interval D designated when the degree of divergence J is at a minimum are extracted.