PURPOSE: To always keep a measuring condition constant, and to obtain measuring data having reproducibility, and also, being comparable thereby by detecting an ultrasonic wave reflected by a subject, or allowed to transmit through the subject, and moreover, comparing a two-dimensional distribution of the ultrasonic wave with a prescribed reference.

CONSTITUTION: In the inside of a measuring tank 20, a subject 18 of a feel (foot), etc., and an ultrasonic matching liquid are contained. Also, on one inner wall in the measuring tank 20, a pair of ultrasonic transducer arrays 21, 22 are provided. That is, for instance, in one transducer array, an ultrasonic wave emitted from an emitting transducer 211, and also, reflected by the subject 18, or allowed to transmit through the subject 18 is detected by a detecting transducer 212. Moreover, a two-dimensional distribution of the detected ultrasonic wave is compared with a prescribed reference, and whether or not their difference is separated above a prescribed value is checked. In such a way, a measuring condition is always kept constant, by which measuring data which has reproducibility, and can be compared strictly with each other.