To provide an easy-to-reuse and eco-friendly differential pressure measuring instrument.

This differential pressure measuring instrument is equipped with liquid-separating diaphragms and liquid-contacting diaphragms. The liquid- separating diaphragms are provided on both side surfaces of a housing, and their peripheral parts are fixed on the housing. The liquid-contacting diaphragms make contact with the liquid-separating diaphragms by one surfaces with a filler liquid interposed between them while make contact with a measured fluid by the other surface. The instrument is characterized by being equipped with backup plates provided opposite to surfaces where the liquid-contacting diaphragms make contact with the filler liquid and remolded by pressing the liquid-contacting diaphragms.