To improve the corrosion resistance, weldability and output characteristic by providing a ring-like thick wall part to be welded and fixed to a body on the peripheral part of a metal seal diaphragm.

Ring-like thick wall parts 31, 32 are integrally provided on the circumferential parts of metal seal diaphragms 33, 34, and the peripheral parts are welded and fixed to main body 1. Since a clearance as blocked by a fluid to be measured in contact thereto is therefore not present in the seal diaphragms 33, 34, the clearance corrosion can be prevented. Since the weld parts to be fixed to the main body 1 formed of the thick wall parts 31, 32, the welding work is facilitated, and a differential pressure measuring device can be manufactured at low cost. Further, since the part of the seal diaphragms 33, 34 can be made foreign to the welding work, the seal diaphragms 33, 34 can be thinned, and a differential pressure measuring device having satisfactory output characteristic can be provided.