An acceleration sensor which detects acceleration by utilizing magnetic coupling. A mass section (3) is displaceably supported by a frame (2) through supporting beams (4). A first planar coil (5) is provided on the section (5), and a second planar coil (8) is so provided as to face to the coil (5) at an interval. A transformer is constituted of the coil (5) as a primary coil and the coil (8) as a secondary coil. The sensor detects acceleration by detecting the variation of the distance between the coils (5 and 8), namely, the displacement of the mass section (3) by utilizing magnetic coupling.