An acceleration sensor comprises an acceleration sensor element having a mass portion in the center, a thick frame surrounding the mass portion and a plurality of elastic support arms bridging the mass portion and the thick frame, and an upper regulation plate covering the acceleration sensor element and fixed on the thick frame with adhesive. The mass portion has, on the mass portion upper surface, connection portions connecting the mass portion with each of the arms, wired areas having lead wires on it and non-wired areas. The non-wired areas have a major area of the upper surface of the mass portion and are lower than the wired areas. The upper regulation plate has a first gap with the wired areas and a second gap with the non-wired areas, of which length is more than the sum of the first gap length, a lead wire thickness and 0.1 .mu.m (preferably 1.0 .mu.m). Even if contaminants adhere the mass portion upper surface, there is a large possibility of removing the contaminants from the upper surface when etching the non-wired areas, so that the vibration amplitude of the mass portion is scarcely lessened due to them.