There are provided a transmitter for transmitting an ultrasonic wave pulse having a definite period toward an object to be examined, a receiver for receiving the ultrasonic wave pulse reflected by the object to produce a corresponding electric signal, a switch for selectively passing the electric signal produced by the receiver, a plurality of delay elements having different delay times and connected to receive the electric signal passing through the switch, and adders for adding the output signals of the delay elements after applying a predetermined weight thereto.