A physical quantity measuring system, includes an optical fiber in which plural fiber Bragg gratings having different reflection wavelength changing bands are formed along said optical fiber in a longitudinal direction, a light source which outputs a broadband light covering the reflection wavelength changing bands of all of the fiber Bragg gratings into the optical fiber, an arrayed waveguide grating which divides a light reflected by the fiber Bragg gratings and outputted from the optical fiber into plural divisional wavelength bands having a constant wavelength interval, and which outputs the divided lights to output channels, respectively, and an operating portion which detects a change of a reflected center wavelength of each fiber Bragg grating by a change of an output of each light-receiving element, and which operates a physical quantity and a position thereof given to the optical fiber, and which is capable of detecting light from adjacent output channels.