A lateral light emitting device that is free from variations and degradation in beam quality and reduction in reliability caused by adhesive, can be easily produced, and has a small diameter in order to be usable for a thin blood vessel and the like is developed.The problem is solved by fusing one end of a rod lens to an end surface of an optical fiber, and by fusing a prism to another end of the rod lens. The prism has a basic shape including a planar light emitting surface parallel to an axis formed by cutting part of a circumference of a cylinder and has a distal end inclined surface, a distal end portion of which is diagonally cut. Alternatively, the problem is solved by fusing a prism lens to the end surface of the optical fiber. The prism lens has a basic shape including a planar light emitting surface parallel to the axis formed by cutting part of a circumference of a cylinder and has a distal end inclined surface, a distal end portion of which is diagonally cut.
