A spring member for an acceleration sensor for detecting acceleration in a direction of a Z-axis that is perpendicular to an X-Y plane includes a movable section having a plane plate shape, for fixing a magnetic field generation member with weight of the acceleration sensor, and a single support arm section having a strip shape parallel to a plane of the movable section when no acceleration is applied. One end of the single support arm section is integrally connected to one end of the movable section and the other end of the single support arm section is fixed. Only the single support arm section in a cantilever configuration supports the movable section.