PURPOSE: To reduce optical loss, to improve characteristics and to reduce production cost of the titled coupler by forming a quadrangular pyramid hole on which a ball lens is to be mounted and V-shaped grooves of which center axis coincides with the center of the ball lens to mount and optical fiber.

CONSTITUTION: The quadrangular pyramid hole 3 is formed on the surface of a silicon single crystal plate 1 by anisotropic etching as an opening surface mounting the ball lens 2. The V-shaped grooves 5, 6 for mounting the optical fiber 4 are formed by anisotropic etching so that their end parts are opened to the quadrangular pyramid hole 3.