PURPOSE: To input first an echo quickly and lessen a fall of a data rate even in case of a large depth by storing received sounded data in a memory and using an idle time zone of reception to reproduce this data in a high speed.

CONSTITUTION: An acoustic sounding machine consists of a transmitter and receiver part 1, a transmitting part 2, a receiving part 3, a depth calculating part 4', a system control part 5', a memory circuit 6, etc. The output of a detecting circuit 33 is given to the calculating part 4' and the circuit 6 through an output line 301. The signal given to the circuit 6 is not controlled by a gate timing control signal received through an output line 502 until the first echo to be discriminated is outputted from a counter circuit 43', and the signal is transmitted to the circuit 43' through a switching circuit 45 and a slicing circuit 41' to calculate the depth. Meanwhile, the condition of the limit of a required reference frequency or the like is considered and set to the circuit 43' for the purpose of reading and reproducing reception signals, which are inputted in echo discriminating time zones, in the idle time of reception.