A three-dimensional acceleration sensor capable of detecting a small acceleration value and even an acceleration value amounting up to 100G occurring in the event of a collision comprises a diaphragm for linking a frame and a massive part and diaphragms and beams for linking the massive part and a central part. These elements are formed by working a single crystalline silicon plate. Gaps between the massive part and opposing electrodes are changed by acceleration applied to the massive part. A circuit connected to terminals detects the changes in gaps as changes in capacitances and determines direction and level of the applied acceleration.