Semiconductor acceleration sensor

A semiconductor acceleration sensor having beam parts formed in substantially L-shape to surround a weight part, wherein formed to surround a square part, as seen in plan view and constituting the weight part, are two elongated L-shaped beam parts, at locations close to proximal end portions of which are formed protruding portions protruding from a fixed part toward the weight part, and receiving recessed portions protruding from the weight part toward the fixed part to surround the protruding portions. The protruding portions have an outer shape substantially the same as an inner wall surface of the receiving recessed portions so that movements of the weight part in any directions in a horizontal direction perpendicular to an up and down direction are limited as a result of reception of the protruding portions by the receiving recessed portions. Thus, even when a side impact is applied to the acceleration sensor, the weight part is prevented from moving significantly, thereby preventing an excessive stress from being applied to the beam parts to break the beam parts.