To enable accurate pressure detection without any influence of environmental conditions of a fluid in a cavity by disposing a silicon substrate opposite to a glass substrate to form a reference pressure chamber.

Silicon substrates 11, 31 respectively include diaphragms 13, 32 which are deformed by fluid pressure to form a movable electrode. A glass substrate 12 having fixed electrodes 16, 35 is clamped by the silicon substrate 11, 32 to be joined to each other to form reference pressure chambers 1, 2. When pressure of a measured fluid is applied to the diaphragm 13, the diaphragm 13 is deformed according to the magnitude of differential pressure from the fluid in the reference pressure chamber 1 to change a gap with the fixed electrode 16. By the pressure of a comparative fluid applied to the diaphragm 32, the diaphragm 32 is deformed corresponding to the magnitude of differential pressure from the fluid in the reference pressure chamber 2 to change a gap with the fixed electrode 35. That is, the difference between the electrostatic capacities C1-C2 produced in the closed reference pressure chambers 1, 2 due to the change in the gap width is computed to detect a pressure difference between the measured a fluid and the comparative fluid.