In order to estimate a temperature of a transmission-reception wavefront of a probe head, a first computing unit and a second computing unit are provided. The first computing unit estimates a temperature TA of the transmission-reception wavefront according to a basic function based on an internal temperature T1, an ambient temperature T2, power consumption Ptotal (=Pic+Ptd), and any other parameter. The basic function is a linear function. The second computing unit estimates a temperature TB of the transmission-reception wavefront according to an auxiliary function based on a previously estimated temperature Tpre, an internal temperature difference ΔT1, and any other, parameter. A selection unit selects any of the temperatures TA and TB depending on situations.