To provide a gas leak alarm which prevents an unexpected accident, possibly caused by use after the reliability guaranteed period, as much as possible.

A time measuring means 21 measures the time after the start of use of a gas detecting element 11a which has its use period determined corresponding to a period wherein the reliability is guaranteed and when the measured time exceeds the mentioned use period, an expiration alarm means 22 notifies that the reliability guaranteed period has expired. Further, when the time measured by the time measuring means 21 reaches a foreseeing period corresponding to a predetermined period shorter than the reliability guaranteed period, a foreseeing alarm means 23 notifies the at the reliability guarantee nearly expires.