To provide a small and inexpensive overload alarm device for a commercial power supply which is used for a small-scale enterprise.

Overload states of a plurality of load facilities 5 connected to a switchboard 4 can be monitored by merely being installed between a main breaker 3 and the switchboard 4. A power factor of the commercial motor power supply is improved, and a load current is prevented by a current regulating capacitor 21 so that the main breaker 3 is inhibited from being cut off immediately, and a time necessary for it to cut off can be extended. Thus, the cutting-off of the commercial power supply can be avoided by taking proper measures such as stopping the undesired operation of the load facility 5 during this time and reducing the load. A small overload alarm device 1 for the small-scale enterprise capable of being easily mounted on the general commercial power supply can be provided at a low cost.