The invention was made to simplify the operation relating to the detection of an absolute pressure applied to a test body by an ultrasonic probe and thereby to enhance usability. The fact that an elastic coupler has been attached to the ultrasonic wave transmitter/receiver surface and the fact that the elastic coupler is in an initial state with no pressure are detected (S2, S3) , an initial thickness of the elastic coupler in the initial state is obtained (S6), the fact that the elastic coupler is in the pressurized state is detected based on the disappearance of a multiple echo which is included in an RF signal and caused due to the elastic coupler, the thickness of the elastic coupler in the pressurized state is obtained by detecting the boundary between the test body and the elastic coupler in the pressurized state, the thickness change is obtained based on the thickness in the pressurized state and the initial thickness (S7) , and the absolute pressure applied to the test object is evaluated based on the thickness change and the pre-set elasticity property of the elastic coupler (S8) .
