To provide a pressure detector which has simple construction and which is easily minimize and lightened and which can detect fluid pressure in particular, hydraulic pressure and the like with desired accuracy.

A silica glass fiber to be a core is bent in U shape by heat processing and its both ends are specularly polished. Solution is prepared by dissolving tetrafluoroethylene-hexafluoropropylene-vinyliden fuluoride ternary copolymer in methylethylketone. Then, the fiber bent in U shape is dipped into this solution and taken out fiber is driednaturally to remove solvent. A clad of 20μm which comprises the ternary copolymer is formed. Both end of obtained optical fiber 2 are mounted through a through hole 41 of a fixture 4 and mounted to terminal parts 3a, 3b. A stainless steel made protecting cover 5 is mounted at a determined position of the fixture 4. The terminal, parts 3a, 3b are respectively connected with an optical power meter of white light source.