PURPOSE: To prevent transmission mistake of a PB signal in advance used for the transmission of a message by monitoring a voltage drop of a battery.

CONSTITUTION: In the transmitter for the pocket bell in which a PB signal in response to a detection signal from various sensors is sent to a radio pager 22 from a transmitter main body 1 via a telephone station 3 and a radio base station 21 to display a message in characters and numerals or the like on a display section 22a of the radio pager 22, a lithium battery 27 is adopted for a power supply of a tone dialer 11 sending a PB signal and a voltage drop detection circuit 20 detects a voltage drop of the PB signal when the PB signal is sent. When the voltage is dropped, a message informing the voltage drop is displayed on the display section 22a of the radio pager 22.