PROBLEM TO BE SOLVED: To automatically differentiate tumor based on volume data collected by a non-contract MRI.SOLUTION: A blood vessel region detecting section 613 of an automatic differentiation unit 6 provided in an MRI apparatus 100 detects a blood vessel region based on time-series volume data of an imaging area collected by blood vessel system units by a selective non-contrast MRI and a tumor candidate region detecting section 621 extracts a voxel having a voxel value larger than a predetermined threshold from voxels in the volume data, and detects a tumor candidate region by extruding the voxels in the blood vessel region out of the voxels. Then, a tumor region detecting section 623 extracts the voxels expressing a TIC (time intensity curve) of a predetermined value or more from the voxels constituting the tumor candidate region to detect the tumor region and a tumor differentiation section 64 differentiates the tumor based on the shape of the tumor region and the voxel value distribution detected by the tumor region detecting section 623.
