PURPOSE: To obtain a compact optical sensor having simple structure and a sensitive measuring method employing it.
CONSTITUTION: The optical sensor 1 comprises a supporting member 2, a corrugated optical fiber 15, and two movable elements 9, 10 fixed to the supporting member 2 to move depending on the variation of the optical fiber 15 and the quantity to be measured. The supporting member 2 is formed as an inboard beam comprising a central part 2a coupled with a membrane 16 operating in response to the variation of measuring quantity, and two end parts 2b, 2c touching two fixed fixing parts 6a, 6b. The optical fiber 15 is set between two movable elements 9, 10 fixed to the two end parts 2b, 2c. The movable elements 9, 10 are provided with working surfaces 9a, 10a touching the optical fiber 15 which is corrugated when the movable elements 9, 10 move.