To provide an abnormality detection device which is easily installed, can detect the occurrence of abnormality without contact and also can be repetitively used, when a light emitter is replaced after the detection of abnormality by using a pawl member which is actuated by the state change of a detection object and the light emitter which emits the light when it is depressed by the pawl member.

A light emitter 1 is fixed to a casing 6 of a sensor main body via an upper cover 5, and a water-absorbing sheet 7 is used to prevent a water absorbing swelling member 3 from leaking to a water-absorbing port 4. A pawl member 2 can move upward by the swelling of the member 3. When an inundation phenomenon occurs, the water enters through the port 4 and reaches the member 3 through the sheet 7. The member 3 can swell only in the upper direction, and accordingly the member 3 swelled by the water pushes up the member 2 and bends the light emitter 1 to make it emit light and to detect the inundation phenomenon. Furthermore, this abnormality sensor itself can be used repetitively, when the member 3 and the light emitter 1 are replaced with new ones respectively, after the inundation phenomenon has been detected.