An optical signal transmission device includes a first and a second photoelectric converting device, a first and a second connector, a plurality of first optical fibers, a plurality of second optical fibers, and an adapter module. The first and the second photoelectric converting devices are electrically connected with the first and the second electronic device. The first and the second connectors separately define a plurality of first and second fixed grooves. The adapter module includes a first and a second adapter portion. The first adapter portion defines a plurality of third fixed grooves. The second adapter portion defines a plurality of fourth fixed grooves. Several optical couplings are generated between the first connector and the first photoelectric converting device, between the second connector and the second photoelectric converting device, and between the first adapter portion and the second adapter portion.