PURPOSE: To make a circuit small-size and enhance reliability, by making the circuit, which converts the dial pulse and so on to a fixed-width pulse, into an electronic circuit.

CONSTITUTION: When dialing is performed in telephone set DPTEL, a pulse voltage is detected in pulse receiving circuit DREC. The pulse voltage is converted to a triangular wave by the integral network consisting of resistance R7 and capacitor C1 and is amplified. The triangular wave is connected to the (-) input terminal of operational amplifier AMP2. The reference voltage is given to the (+) input terminal of AMP2; and if the triangular wave is higher than the reference voltage, an output is generated in AMP2 to turn on transistor TR, and relay RL0 is operated. When the triangular wave is equal to or lower than the reference voltage as the result of receiving of the dial pulse, relay RL0 is released, and one pulse is taken out from relay RV0.