PURPOSE: To lessen loss of light combination and to improve efficiency of light utilization by forming a branching part by contacting and combining plural optical fibers with each other and providing a heating element in the branching part.

CONSTITUTION: Optical fibers 1, 2 are buried on the surface of a base plate 4 made of an epoxy resin in a state that they are connected to each other at a part of them and the connected condition is fixed. Further, a heating element 3 is provided on the surface of the substrate 4. When a current pulse is applied to the heating element 3 to generate heat, the heat is transmitted to clad parts 11, 21 of the fibers 1, 2, and the refractive indices of clad parts 11, 21 become nearly the same as those of core parts 10, 20 due to rise of temperature in the area 30. Accordingly, when light is being transmitted in the fiber 1, the light is transmitted from the fiber 1 to 2 from the core part 10 through clad parts 11, 21 where the refractive indices are raised, and the waveguide path of the optical fiber 1 and that of the optical fiber 2 are combined to each other.