TELEPHONE SET WITH AUTOMATIC SOUND RESPONSE FUNCTION

PURPOSE: To prevent the malfunction of a hand-free function by setting a system to be an incoming call state when the sound signal level of a sound frequency, which urges an incoming call, is judged to exceed a threshold level. CONSTITUTION: Noise at a periphery where a telephone set is installed is always detected by an A/D converter 33 being a noise level detection means, and an average value processing circuit 36, a sound field comparison circuit 37 and a threshold deciding circuit 38, which are threshold level deciding means, decide the threshold level corresponding to the level of noise. A sound judgement circuit 40 judges whether the sound signal level of the sound frequency, which urges the incoming call, exceeds the threshold level or not after a level signal arrives at a line. When the sound signal level of the sound frequency, which urges the incoming call, is judged to exceed the threshold level, the system is set to be the incoming call state. Since the system becomes the incoming state only when the sound signal level of the sound frequency, which urges the incoming call, exceeds the threshold level, noise is prevented from being recognized as the sound urging the incoming call.