Real-time display of a three-dimensional ultrasonic image in which there is little time delay, power required for transmission of an ultrasonic wave is reduced, and heterogeneousness of received beams is almost solved is performed by executing multi-beam reception while performing frequency demodulation of a reflected wave obtained as a result of transmission of a frequency-modulated continuous ultrasonic wave to the subject body. As a demodulation method, for example, a multi-phase demodulation method of obtaining the distance resolution in multi-beam reception by performing (multi-phase) demodulation while changing the phases of transmission modulation and reception modulation for every range in the range direction (beam direction).