To provide an alarm device that prevents a switch for starting alarm operation from being broken caused by being drawn by an operating knob.

An engagement body 16 is fitted to an end of the strap 14 so as to couple the operating knob 15 outside a main body to a switch 13 provided in the main body to start alarm operation with the strap 14, and a recessed portion 17 for engagement wherein the engagement body 16 is stored to engage it is formed on the operating knob 15. A breaking portion 19 which breaks when tension which is not large enough to break the switch 13 is applied to the strap 14 after the switch 13 is operated is formed at the engagement portion between the engagement body 16 and recessed part 17 for engagement, and even when the operating knob 15 is drawn strongly owing to an abnormal state, the break part 19 breaks before the switch 13 breaks, thereby separating the operating knob 15 and strap 14.