An optical fiber, which is provided in each of channels of an optical fiber array disposed on V-grooves, has a portion (reflecting section) at which a core is cut out at an intermediate position of the optical fiber. The reflected light, which is split from a signal light transmitted in the core of the optical fiber on the basis of a refractive index difference at the reflecting section, is obtained through a index matching layer provided outside a clad of the optical fiber. The reflected light is monitored by a photodetector of a photodetecting array.