a pressure sensor has a recess formed in outer surfaces of a deforming part and a non - deforming part such that a pair of steps are formed at opposite ends of the recess . the deforming part is strained by a pressure whereas the non - deforming part is not strained by the pressure . an amorphous magnetic alloy film is received in and affixed relative to the recess , and extends between the pair of steps . the depth of the recess is larger than the thickness of the film . a pair of permeability detector elements are mounted respectively on the deforming part and the non - deforming part so as to detect a change in permeability of the film .