To improve manipulation safety by providing a projecting part project ing from a pressure-receiving flange and narrowing a central part of a recess, and reducing a difference of sectional areas between a central part of a flange chamber and the vicinity of a pressure introduction opening.

A block part comprises a high pressure body 1, a low pressure body 2, a high pressure liquid-separating diaphragm 4A, a low pressure liquid- separating diaphragm 4B, a center diaphragm 3 and a sensor 8, etc. Recesses 21A, 21B are formed at one side of the high pressure body 1, low pressure body 2, which is not in touch with the body 1, 2 even when the center diaphragm 3 is deformed to the maximum. Pressure-receiving flanges 12A, 12B guide a measurement pressure from pressure introduction openings 16A, 16B to the liquid-separating diaphragms 4A, 4B. Conical projecting parts 23A, 23B are provided at bottom parts of the recesses 21A, 21B of the pressure-receiving flanges 12A, 12B. In the configuration, a difference of sectional areas between a central part of a flange chamber and the vicinity of the pressure-introduction opening is reduced, so that a pressure difference in the flange chamber is decreased.