To provide an apparatus for measuring differential pressure, which is improved in zero drift caused by plastic deformation remaining in a protection diaphragm after applying excessive pressure thereto, by controlling stress produced in the protection diaphragm.

When the excessive pressure acts on seal diaphragms 6A (6B), which seat on waveform surfaces of right (left) in an apparatus body 5A (5B), liquids LQA (LQB) enclosed in seal diaphragm chambers 8A (8B) are dispersed and moved into protection diaphragm chambers 9A (9B) and 10A (10B). Consequently, the displacement of protection diaphragms 4A (4B) is reduced more than that of a sheet of protection diaphragm, which reduces the stress developed in the protection diaphragm, and accordingly, the plastic deformation remaining in the protection diaphragm is reduced after applying the excessive pressure.