In an embodiment of the present invention, a category dividing unit (150) divides each image constituting time-series in-vivo images, which are captured by a capsule endoscope moving through a lumen in a body, into category areas including a mucosa area and a lesion candidate area. An OF (Optical Flow) calculator (154) calculates optical flows of the mucosa area and the lesion candidate area. The lesion area detecting unit (155) detects a lesion area by comparing the optical flows of the mucosa area and the optical flows of the lesion candidate area.
