To improve an optical device, such as an optical pressure sensor and the like in the detection accuracy and in the manufacturing efficiency.

The optical pressure sensor 1 comprises an optical waveguide 3 formed on one substrate face of a silicon substrate 2, a pressure-receiving chamber 5 formed on the other substrate face, and a diaphragm 6 formed at the bottom of the pressure-receiving chamber 5. That is to say, the optical waveguide 3, the pressure-receiving chamber 5 and the diaphragm 6 are formed integrally into a single silicon substrate. Thus, when the pressure of a fluid flowing into the pressure-receiving chamber 5 causes displacement of the diaphragm 6 in the vertical direction or the like, the displacement is transmitted to a Bragg grating 4 precisely and directly, whereby the pressure of the fluid can be detected with high accuracy and with good response.