A handheld telephone set used by connecting a dual-ear mount type or single-ear mount type earphone that automatically sets an optimal signal level of an ambient sound according to the earphone type used, provided with: a telephone set main body unit, a detection device for detecting which type of earphone is mounted to the telephone set main body unit, an amplifier for amplifying the ambient sound to be delivered to the earphone, and a control device for controlling a signal level of the ambient sound output from the amplifier according to an output of the detection device. When either of these earphones is mounted, the control device controls the signal level of the ambient sound output from the amplifier to be fed back according to an output of the detection device.