PURPOSE: To issue warning and to acquire the location of a user when the electric field strength is deficient and a reception available area is deviated.

CONSTITUTION: A frame synchronizing signal sent from a transmission station is received by a radio wave reception section 11 and demodulated by a demodulation section 12 and the frequency synchronizing signal being the output of the demodulation section 12 is collated by a synchronization latch circuit 14 at a prescribed interval to hold the synchronization. A CPU 15 activates an intermittent reception timer 16 during this time to activate an intermittent reception operation control circuit 21, which collates an identification number inherent in a receiver stored in an IDROM 13 with an identification number sent from the transmission station. When the result of collation of the frame synchronizing signal is discordant, the synchronization holding by the synchronization holding circuit 14 is released and a synchronization holding monitoring timer 17 gives an output to drive an alarm driving informing circuit 18 by the CPU 15, thereby allowing a warning sound to be outputted from a sounder 19.