To provide an alarm device where a plurality of portable transmitters can be combined with one receiver driving the alarm device, thus making it possible to secure all employees at all times.

The alarm device drives an installed alarm 15 via a receiver 5 under control of a portable transmitter 1 by radio. The receiver 5 has a reception control circuit 12 which can identify and register a plurality of transmitters 1A-1D having different authentication codes ID1-ID4. The receiver 6 driving the alarm 5 can be operated from the plurality of portable transmitters 1A-1D allocated only to members. All the employees who are the members are given the portable transmitters 1A-1D for security. In addition, tampering using portable transmitters owned by people other than the members can be prevented.