To inexpensively provide an optical directive coupler unnecessary for adjustment (consequently strong in vibration).

The optical directive coupler (10) obliquely protrudes a ramal part (12) comprising a transparent raw material on the side of a columnar part (11) comprising the transparent raw material making one end face an optical incident and emission face (13) and making the other end face an optical emission face (14) at a prescribed angle, and composes the end face of the ramal part as an optical emission face (15). The optical directive coupler sets a protruded angle (prescribed angle) of the ramal part so that in each side of a columnar part an opposite face of the protruded face of the ramal part out of each side of the ramal part acts as an optical light guide face (16) applied on the incident face.