PURPOSE: To remove an unnecessary part from a lot of slice pictures in a short time by subtracting the three-dimensional data of the unnecessary part from three-dimensional data, for which a relative position is adjusted, to be a processing object and displaying the data on a screen.

CONSTITUTION: Reference data 10 (three-dimensional picture data) of a head rest are stored in a reference data storage part 1 and processing data (three- dimensional picture data) 11 are stored in a processing data storage part 2. In such a state, when a command for removing the unnecessary part is inputted from an operation part 4, a picture processing part 3 reads out the processing data 11 stored in the processing data storage part 2 and the reference data 10 stored in the reference data storage part 2. Afterwards, the picture processing part 3 subtracts the reference data 10 from the processing data 11, prepares three-dimensional picture data 12 removing the unnecessary part and displays these data 12 on a display part 5. Thus, without executing trace work, the unnecessary part can be removed from a lot of the slice pictures in a short time and burden on a user side can be reduced.