To provide a microphone/speaker for portable telephone having a microphone and a speaker enabling bidirectional speaking through a connection to a portable telephone, with which the voices of a party can be clearly heard even at a place surrounded with noises and further which does not generate howling.

Concerning the microphone/speaker for portable telephone to be used while being connected to a terminal 2 for earphone/microphone of a portable telephone 1, this device has a speaker 4 provided with an output amplifier 3, a microphone 5 and a changeover switch 6 for switching electrification to these speaker 4 and microphone 5 and by switching the changeover switch 6, speaking is enabled while alternately turning on/off the speaker 4 and the microphone 5.