PURPOSE: To put a device into practical applications by laying out a plurality of ultrasonic probes while the mounting angle is inclined by a directional angle.

CONSTITUTION: For example, three ultrasonic probes 3a, 3b, and 3c for dipping in water are mounted to a holder while the mounting angle is inclined by a directional angle under a water surface 1 where an object 2 in water exists and at the same time the ultrasonic probes 3a, 3b, and 3c are connected to a pulser receiver 5 outside the water surface 1 in parallel. By laying out three ultrasonic probes 3a, 3b, and 3c in this manner, either one of the ultrasonic probes :3a, 3b, and 3c detects the inclination of the object 2 in water by πθ, thus measuring the distance with the object 2 in water. Therefore, by using the device, the range of distance in water for several m can be measured without any practical problems.