To ensure that a pair of voice input/output parts mounted in a handset are switched to the receiver or the transmitter with appropriate timing.

One of voice input/output parts which is detected to be upper by an upper/lower detection part 4 when voice is detected by voice detection parts 5A, 5B is made a receiver and the other is made a transmitter, so that the detected voice is determined to be the voice of the user. Therefore, when the upper/lower direction is detected by a handset 1 at that point of time, there is high possibility that the user has placed the handset 1 at a conversation possible position. Accordingly, even when the user has changed the direction of the handset 1 before he places the handset 1 at a conversation possible position after grasping it in his hand, detection by the upper/lower detection part 4 is not executed, and the upper/lower detection is executed when the handset 1 is placed at an appropriate position, so that the voice input/output parts 3A and 3B can be switched over with appropriate timing. Also, since determination is made by voice detection, appropriate detection is possible even when the handset 1 is in a high temperature environment.