A photoelectric conversion device includes a circuit board, a light emitting module, a light receiving module, and an optical coupling lens. Two protrusions apart from each other extend from the circuit board. The light emitting module and the light receiving module are mounted on the circuit board and apart from each other. The optical coupling lens includes an oblique reflection surface and a recess having a bottom surface parallel to the circuit board. Two distanced posts perpendicularly extend from the bottom surface and engage with the centers of the protrusions upon assembly to ensure automatic and alignment of the light emitting module with the first converging lens, and alignment of the light receiving module with the second converging lens.