A tissue-image creating unit creates a tissue image including depth values by volume rendering from three-dimensional tissue data stored in a three-dimensional data storage unit. A blood-flow data converting unit scatters a blood flow in three-dimensional blood-flow data stored in the three-dimensional data storage unit into particles, and converts the three-dimensional blood-flow data into three-dimensional particle data. A blood-flow image creating unit creates a blood-flow image including depth values from the three-dimensional particle data. A composite-image creating unit then creates a composite image by coordinating the order of rendering particles and tissue based on the depth values of respective pixels included in the tissue image and the depth values of respective particles included in the blood-flow image. A display control unit then controls display of the composite image so as to be displayed in order onto a monitor included in an output unit.