PURPOSE: To prevent automatically the use of a telephone with no agreement of the telephone owner by inhibiting the calling when a binary code corresponding to the inhibiting dial number is supplied.

CONSTITUTION: The dial pulse of a telephone 10 is detected 24 and converted 130 into a binary code, and an inhibition signal is generated 120 to inhibit the calling when the binary code corresponding to an inhibited dial number is supplied. At the same time, a control signal is produced 110 for a prescribed period to enable the calling when the binary code corresponding to a specific dial number is supplied. Then the inhibition signal is prevented by a gate 138 in response to said control signal. At the same time, a telephone line is cut off by a switch 144 in response to the inhibition signal which passed through the gate 138.