PURPOSE: To connect an optical fiber to a planar optical waveguide integrated on a board protruded into a groove with a little connection loss by arranging the end face of the planar waveguide at the end of protruding part of the board and tightly connecting the end of this protruding part to the end face of the fiber.

CONSTITUTION: An end face 21 of a planar waveguide 2 is arranged at an end 21 of protruding part 5 of a board 1 protruding into a groove 3 so that the end 21 of the protruded part 5 can be tightly connected to an end face 41 of a fiber 4. Namely, a terminal area 34 of the groove 3 is prepared isotropic etching and the protruded part 5 is formed by undercutting the end face 21 of the planar waveguide 2 in this area. By forming the protruding part 5, the end face 41 of the fiber 4 inserted into the groove 3 can be tightly connected with the end face 21 of the planar waveguide 2. Thus, the fiber 4 and the waveguide 2 can be abutted and connected with a little attenuation.