A fiber-type optical coupler has two optical fibers including a core on which a slanting Bragg diffraction grating is formed and a first cladding and a second cladding bordered with a boundary plane close to the core. The two optical fibers are placed by approximating the boundary plane almost contacting the core, making respective optical axes almost parallel and also making slanting directions of the respective Bragg diffraction gratings almost parallel. A wave vector of the slanting Bragg diffraction grating is located in a plane made by a normal set up on the boundary plane almost contacting the core and the optical axis of the core, and an angle_made by the wave vector and the optical axis is 0 degree <_<90 degrees. In addition, a refractive index of the second cladding is lower than that of the first cladding.