PURPOSE: To shorten measurement time and simplify measurement by placing a supersonic wave transmitter/receiver fixed to a wedge having a curved face on an end of a pipe and calculating length of the pipe from propagation time required for reciprocation, which is to be displayed.
CONSTITUTION: A supersonic wave transmitter/receiver 1 is inserted into a pipe hole, and with a switch of an operation setting unit 18 turned ON, a burst pulser 11 outputs a burst pulse to the wave transmitter/receiver 1. The wave transmitter/ receiver 1, in response to a pulse signal from the pulser 11, transmits supersonic waves from a piezoelectric vibrator 5 and propagates the supersonic waves from a curved face 3. The vibrator 5 receives the supersonic waves reflected on an end of the pipe and returned. The received supersonic waves are sent via a receiver 12 and a time measuring gate 13 to a counter 15. The counter 15 counts the number of pulses of clock pulses of the gate 13 and measures propagation time of the supersonic waves. Thus time required for measuring length of an object to be measured is short and measurement is easy.