To provide a diaphragm-seal type differential pressure measuring device, having design freedom less susceptible to standardized size of a gasket and enhancing measurement accuracy and temperature characteristics.

The diaphragm-seal type differential pressure measuring device having a diaphragm seal unit with wetted seal diaphragm and a gasket 8, one side surface of which has contact with the wetted seal diaphragm and the other side surface of which has contact with a mounting flange 9 of a measuring object is characterized, by including a ring-shaped protection plate 31 prepared between the gasket and the pressure receiving diaphragm 7 and a protective ring 32 prepared between the gasket and the pressure receiving diaphragm 7 to fix the external diameter to the inner diameter of the protective plate 31, where the inside diameter is identical with or is smaller than that of the gasket.