A single-element ultrasonic sensor includes a single transducer element and transmits an ultrasonic wave on the basis of a pulse wave. An ultrasonic array sensor includes a plurality of transducer elements and receives an ultrasonic reflected wave. A pulsar supplies the pulse wave to the single element ultrasonic sensor. A receiver receives electric signals from the transducer elements included in the ultrasonic array sensor. An amplification and conversion unit amplifies the electric signals received from the transducer elements included in the ultrasonic array sensor, converts the electric signals into digital signals, and arranges the digital signals in a serial order so as to generate a serial digital signal. An image generator generates an image on the basis of the serial digital signal.