The receive sensitivity of an ultrasound array transducer structured with a diaphragm electro-acoustic transducer (101) being a basic unit is affected by change in a charge amount with elapsed time due to leakage or the like, which causes drift of the primary beam sensitivity, degradation in the acoustic SN ratio due to a rise in the acoustic noise level, and degradation in the directivity of an ultrasound beam. To addressing this problem, a charge controller (charge monitor 211) is provided to control charge in an electro-acoustic transducer (101). A charge monitoring section (102) monitors the change in the charge amount. When change in the charge amount is small, transmit sensitivity or receive sensitivity is calibrated by a controller (104) by, for example, multiplying a receive signal by a calibration coefficient corresponding to the change amount. Further, when the change in the charge amount is large, for example, charges can be re-emitted from a charge emitter (103).