An miniaturized accelerometer having a narrow bandwidth and behaving as a switch sensitive only to low frequencies such as contained in earthquakes includes: a unbalanced see-saw beam assembly composed of beams 2 and masses 3 at opposite ends of the beams 2. The beams 2 have their suspension at a location with slightly different distances from the masses 3 along a line parallel to and vertically offset from the line connecting centers of gravity of the masses 3.