PURPOSE: To replace a driving battery for a mobile radio communication equipment with a standby battery without interruption of operating communication by devising the standby battery and the other standby battery to be attached/ detached to/from the equipment.

CONSTITUTION: When communication is made while an attachable/detachable battery 2 is attached to a mobile radio communication equipment, a microprocessor 6 controls a voltage detection circuit 5 to discriminate whether a power supply voltage supplied during the communication is a drive enable voltage or a drive disable voltage and gives information to an alarm tone generating circuit 7 when the voltage is discriminated to be a drive enable minimum voltage to allow a sound generator 86 to generate an alarm tone thereby informing it to the user that the communication is disable by the attachable/detachable battery 2 used in this communication. When the user desires the extended communication furthermore, the battery 2 is replaced with a standby attachable/ detachable battery 3 and power is supplied to the mobile radio communication equipment from the standby attachable/detachable battery 3 to continue the communication.