PURPOSE: To improve the operability and the measuring accuracy by eliminating the need of adjusting a tuning coil when coaxial cables different in length are connected to each other.

CONSTITUTION: An ultrasonic propagation time measuring device 10 is so constructed that an ultrasonic vibrator 72 for generating an ultrasonic wave and a tuning circuit 12 for matching the impedance of the ultrasonic vibrator 72 and supplying the power for oscillation to the ultrasonic vibrator 72 are provided on an ultrasonic head 14. A propagation time measuring circuit 78 to which transmit/receive signals of the ultrasonic vibrator 72 are input to measure the propagation time is provided on the main body 16. The coaxial cables 82a, 82b for transmitting transmit/receive signals of the ultrasonic vibrator 72 connect the propagation time measuring circuit 78 of the main body 16 and the tuning circuit 12 of the ultrasonic head 14 to each other.