To achieve high accuracy by setting one face of a single crystal silicon substrate at a face of a polysilicon layer formed at one face of another single crystal silicon substrate having a recessed part, and setting a strain sensor to an obtained diaphragm.

A polysilicon layer 12 is formed in a semiconductor process to one face of a single crystal silicon substrate 11, and a single crystal silicon substrate 13 is set at the other face of the polysilicon layer 12 into face-to-face contact with each other. A diaphragm 14 is thus constituted together with the polysilicon layer 12. A recessed part 15 is formed at the side of the one face of the single crystal silicon substrate 11 to form the polysilicon layer 12 and a gap chamber 16. For instance, a strain detection element 17 or the like piezoelectric resistance strain gauge is set at the diaphragm 14. A pressure guide hole 18 communicates with the gap chamber 16 through the single crystal silicon substrate 11 or the other face of the single crystal silicon substrate 13. In this structure, influences of a residual strain of the polysilicon layer 12 are reduced, the diaphragm 14 can be thinned, and measurement accuracy, sensitivity characteristic are improved.