PURPOSE: To provide a convenient device for plural persons to confirm the position of a party each other in the water concerning a radio transmitter/ receiver to be used in the water.

CONSTITUTION: This device is provided with a means for measuring an event correlated with the depth of water, converting this event to the depth of water and outputting it as depth information, transmission part 10 for letting the depth information and a device number allocated to the relevant radio equipment ride on the radio wave of a fixed output and transmitting it while using a previously decided slot, reception part 11 for receiving the radio wave of the previously decided slot at a prescribed frequency, distance display part for measuring the reception level of the received radio wave, converting that level into distance information and displaying it, and depth display part for detecting and displaying the information concerning the depth of the received radio wave and the device number.