To provide a 'cellular telephone system' with which safe vehicle driving is ensured and automatic reply with respect to an incoming call is attained.

In the system to the main body of which a telephone set 16 is set, an external microphone 15 placed in a cabin picks up voice information and an external speaker 14 placed at the outside of the cabin provides an output of the voice information. In this case, the system is provided with a control mode detection means 13 that detects a drive operation mode requiring attention. In the case that an incoming call signal is received when the control mode detection means 13 detects a drive control mode requiring attention, without call tone being outputted, a message denoting it is delivered to an opposite party.