PURPOSE: To beforehand prevent an accident while a gas alarm rings normally at the time of leaking the gas by promoting the connection with the external power with a sound signal while the supply of the electricity from the external power is discontinued.

CONSTITUTION: While the connection with the external power is discontinued, to sound functions 16-18 equipped at a usual gas alarm, a power connection evoking means 19 to generate a sound signal to promote the connection to the external power in order to cancel the condition is added. Here, the power connection evoking means 19 starts this with the sound functions 16-18 at the time of necessity and generates the sound signal. Then, for example, the housewife at the kitchen hears the sound signal, recognizes that the gas alarm is discontinued from the external power and performs the connection with the gas alarm and the external power.