Fluid parameters such as WSS and EL are accurately calculated, using flow velocity information obtained by diffusion tensor imaging. Dispersion of a flow velocity distribution of fluid is calculated, using a diffusion tensor image obtained with respect to an examination target containing fluid, and an estimation model is set for a distribution shape of intra-voxel flow velocity. Using the estimation model and the dispersion of the flow velocity distribution, a differential value of the flow velocity is calculated. Then, a fluid parameter representing a flow characteristic of the fluid is calculated.