An acceleration sensor includes a weight; a base portion, a beam; and a piezo resistance element. The weight is arranged to displace upon receiving acceleration. The base portion is disposed around the weight apart from the weight. The beam has one end portion connected to the weight and the other end portion connected to the base portion. The beam also has a thick layer portion and a thin layer portion having a thickness smaller than that of the thick layer portion. The piezo resistance element is disposed over the thick layer portion and the thin layer portion.