To obtain an optical transmission device having a relatively simple constitution eliminating the necessity of having a directional coupler and an optical phase shifter and an optical tap and/or an ADD functions are realized.

The optical transmission device consists of an optical transmission line 21 having a bent section 21a and at least one of a light receiving element 31, which is provided in the vicinity of or contacting to the section 21a and receives light beams 22 that are leaked from the section 21a, or a light emitting element which is located in the vicinity of the section 21a or contacting to the section 21a and introduces light beams to the line 21. A radiation mode exists at the section 21a of the line 21 and the light beams are received by the element 31. The light beams radiated from the light emitting element are coupled to the line 21 through the section 21a of the line 21.