1. An ultrasonic transducer, comprising:a housing that internally includes an ultrasound transmitting/receiving unit, and the housing sealing an ultrasonic propagation liquid;
a driving device that includes a driving motor and a drive shaft which is an intermediate member rotationally driven by the driving motor, the driving device being configured to transmit a rotary driving force from the driving motor to swing the ultrasound transmitting/receiving unit; and
a detecting device that includes a detecting member and is configured to detect an origin position serving as a reference in control of a swing of the ultrasound transmitting/receiving unit, wherein
the driving device is configured to transmit the rotary driving force to the intermediate member,
the drive shaft is disposed such that one end portion of the drive shaft enters an interior of the housing and transmits the rotary driving force to the interior of the housing,
the detecting device being configured to extract a rotation of the intermediate member outside of the housing, a reduction element being configured to decelerate the rotation of the intermediate member and transmit the rotation which is decelerated to the detecting member of the detecting device in a route different from the driving device, and the detecting member is rotated at a first rotation speed lower than a second rotation speed of the drive shaft, and the detecting device being configured to detect the rotation of the detecting member by a sensor to detect an origin position.