PURPOSE: To obtain an audible signal tone detecting circuit which has good detection precision and takes a short time for detection, by providing two memories, a read address circuit, a comparing circuit, and a deciding circuit.

CONSTITUTION: When a digital code sequence for showing an audible signal tone to be detected is applied to an input terminal 23 and does not coincide with an output code of a memory 20, the output of a memory 28 is fetched in a read address circuit 21 immediately and outputted to the memory 20. The output code of the memory 20 then coincides with the received digital code and the read address circuit 21 goes up according to a sampling clock. The memory 20 outputs a digital code correspondingly, but its output coincides with the received digital codes completely, so while the audible signal tone to be detected is applied to the input terminal 23, a comparing circuit 22 outputs "1" continuously. A deciding circuit 29 decides on that. Thus, the audible signal tone detecting circuit has high detection time and short detection time.