PURPOSE: To make such temperature information that is high in reliability securable by discriminating a possible area to give unrighteous temperature information from the other area on the basis of two tomographic images, and specifying it clearly.

CONSTITUTION: After a tomographic image is secured on a slice surface 41 before heating, another image is also secured on a slice surface in a position somewhat different in a slice thickness direction to this slide surface 41 without delay. Then, such an area that each picture element value of a difference image between these images is larger than the specified threshold value is specified as a possible area as giving unrighteous temperature information. Next, another image on the slice surface 41 before and after warming a patient 4 with a warming unit 2 is secured, and subtraction between both these images is carried out and thus distribution of a temperature change is secured.