OPTICAL TRANSMISSION DEVICE

PROBLEM TO BE SOLVED: To provide an optical transmission device capable of sure protection against entry of foreign matters and the like from a plug inserting hole without using a protective cap that requires removal and storage. SOLUTION: In the optical transmission device equipped with an optical element 14 that performs at least either light receiving or light transmitting and with a support 10a, 10b that, holding the optical element 14, carries out optical coupling when the plug 13a of an optical fiber cable 13 is inserted into the plug inserting hole 12; the device is constituted such that the inner face of the plug inserting hole 12 is formed with a groove 17 corresponding to a belt-like projection 13b on the side of the plug 13a of the optical fiber cable 13, and that a shutter 11 is provided which opens/closes inside the plug inserting hole 12, with the rotary shaft 16 functioning in a direction nearly vertical to a line connecting between the groove 17 of the plug inserting hole 12 and its inner face oppositely facing the groove 17.