[Problem] To shorten the processing time required when extracting a region from an image using a graph cut method, and reduce the amount of memory used for computation. [Solution] An image acquisition unit (10) acquires a plurality of CT images from an X-ray CT device (2) and generates a three-dimensional image (M0). A low-resolution image generation unit (12) converts the resolution of the three-dimensional image (M0) into multiple resolutions and generates a low-resolution image (ML). A first extraction unit (14) uses a graph cut method to extract a specific region such as a liver region from the low-resolution image (ML). A contour region setting unit (16) sets the contour of the liver region extracted from the low-resolution image (ML) in the three-dimensional image (M0), and sets a contour region including said contour in the three-dimensional image (M0). A second extraction unit (18) extracts the contour of the liver region from the contour region, and extracts the liver region from the three-dimensional image (M0).
