To provide a wireless transmitter/receiver set for a portable telephone, where the power consumption when waiting is reduced for extended battery life even when a small and light-weight low-capacity battery is used, and to provide a wireless transmitter/receiver which is worn in a user's ear for calling as a slave device of a fixed telephone and a portable information terminal device having telephone function.

The unit of a wireless transmitter/receiver set for a portable telephone comprises a means for periodically detecting reception of radio waves from a head set, and a means which supplies electric power to a transmission/ reception part from a power source battery when the detecting means detects reception of the radio wave, while cutting off the power when it does not detect radio waves. The wireless transmitter/receiver set in which a microphone and an earphone are built is supplied with power from a built-in battery and is used as a hands-free slave device for a fixed telephone or a portable information terminal device.