A coupling structure between a fiber and an optical waveguide to couple the optical waveguide to the fiber is disclosed. A substrate includes an optical waveguide region and at least one aligning groove for containing the fiber. The optical waveguide region has optical circuits and input/output surfaces of the optical circuits. The input/output surfaces face the aligning groove. A non-perpendicular angle is formed between input/output surfaces and the progressing direction of the incident light.