Abstract: A telephone line state detecting device that is connectedly provided with a hardware detecting circuit when a telephone line is connected to a modem. The hardware detecting circuit is connected to a processing unit such that, in use, the hardware detecting circuit can detect pulses generated by voltages flowing through the telephone line. The pulses are being processed by the processing unit to judge whether the telephone is disconnected or the electrical contact thereof is deficient, or whether the telecommunications equipment used in conjunction therewith is busy or not in use.