A body movement signal generation unit (60) generates a body movement signal which varies in response to body movement of a test subject as a diagnosis subject on the basis of a reception signal corresponding to a monitoring reception beam obtained from a reception unit (14). A body movement monitoring unit (62) determines the start time of a diagnosis-recommended period in which body movement is minimal by distinguishing between large and small body movements on the basis of the body movement signal obtained from the body movement signal generation unit (60). A control unit (70) executes diagnostic processing from a start time for diagnosis. Through this configuration, it is possible to obtain stable diagnostic information in which the effect of heartbeats is low and that is preferably entirely unaffected by heartbeats.
