PURPOSE: To make the display of the sea bottom three-dimensional, by radiating acoustic waves upon the sea bottom from an advancing platform, with a wave transmitter-receiver mounted on the platform, displaying the contour lines of the sea bottom by superposing the contour lines upon a two-dimensional continuous record.

CONSTITUTION: A command signal is sent from a command signal transmitter 31. Upon receiving the command signal, the transponder 18 of a towed body 500 responds and sends a response signal. After the response signal is caught by a 3-channel wave receiver 32, a relative position information calculator 33 calculates and outputs relative position information, such as distance, bearing, dip information, etc., to the towed body 500 in accordance with the conditions, such as the phase difference between each receiver output, responding time interval, or relative position between each receiver, etc., and supplies the information to a coordinate setting section 4. The setting section 4 calculates and sets so that the sea bottom prospecting data and contour line data can be displayed on a common coordinate system under a superposed condition by utilizing the ship position information and relative position information to the towed body 500 thus inputted, and the data are stored in a picture image memory 5 under a classified condition. A display section displays the contour lines upon the sea bottom prospecting data under the control of a display controlling section 7.