A free fall sensor includes an electrically conductive container, an electrically conductive pin having an end inserted into the container, and a movable electrode enclosed in the container, the movable electrode including a coil spring cantilevered on the end of the conductive pin and a weight disposed in an inner space of the coil spring so as to be movable and so as to be prevented from falling off. The weight is a sphere having a smaller diameter than the coil spring.