In a MEMS device having a substrate 1, a sealing membrane 7, and a movable portion 3 of beam and an electrode 5 which have a region wherein they overlap with a gap in perpendicular to a substrate 1 surface, a first cavity 9 is on the side of the movable portion 3 in the direction perpendicular to the surface of the substrate, and a second cavity is the other cavity, and an inner surface a of a side wall A in contact with the electrode 5, of the first cavity 9, is positioned more inside than an inner surface b of a side wall B in contact with the electrode 5, of the second cavity 10, in the direction parallel to the substrate surface, such that the movable portion 3 does not collide with the electrode 5 when mechanical stress is applied from outside to the sealing membrane 7.