Abstract: It is an object of the present invention to provide a portable telephone in which external sound can be used as a call receiving sound and a pause of sound can be avoided even when the switching operation of a base station is generated during reproducing the call receiving sound. Sound picked up by a microphone (180) is subjected to an AD conversion, then encoded by an ADPCM system in an encoding part (141) and stored in an ADPCM encoded data storing area (150b). The stored audio data of a partner to talk with is encoded by the ADPCM system in the encoding part (141) via a digital audio signal processing part (122) and stored in the ADPCM encoded data storing area (150b). Upon receiving a call, the stored data is read, decoded to an analog audio signal in a decoding part (142) and outputted as the call receiving sound from a speaker (181) via an audio output circuit (136).

Abstract: Temperature measuring unit measures an ambient temperature and outputs a measurement result to control unit. The control unit outputs information for optimally setting the number of boosting stages of boosting unit as a control signal to driving circuit. Upon receipt of the control signal, the driving circuit stores the information in storage unit, sets the number of boosting stages of the boosting unit according to the information stored in the storage unit, and supplies a driving voltage to liquid crystal display unit. If the ambient temperature is changed, the number of boosting stages of the boosting unit is reset in the procedure so that the consumed current of the whole liquid crystal display device can be optimized.