Magnetic resonance imaging device

A magnetic resonance imaging apparatus comprising:

• a measurement part that acquires a plurality of diffusion-weighted images by applying a diffusion gradient magnetic field pulse in a plurality of different directions defined beforehand according to a predetermined imaging pulse sequence, and
• an image analyzer that detects presence or absence of body motion of a subject under imaging using the plurality of the diffusion-weighted images, wherein:
• the image analyzer comprises:
• a group creator that creates a plurality of image groups each including 6 or more diffusion-weighted images selected from the plurality of the diffusion-weighted images so that the groups differ from one another in one or more of the included diffusion-weighted images,
• a diffusion index calculator that calculates value of a predetermined diffusion index that represents a characteristic amount of diffusion-weighted image for each of the image groups from the diffusion-weighted images included in that image group,
• a body motion index calculator that calculates value of a predetermined body motion index concerning body motion information from the value of the diffusion index for each of the image groups, and
• a body motion detector that determines presence or absence of body motion for each of the image groups on the basis of the value of the body motion index.