The present invention provides an optical transmission device configured from a case that holds an optical element that receives and/or transmits light, the case being provided with a plug insertion hole into which a plug for transmitting an optical signal is inserted; and a shutter mechanism having a shutter that opens and closes the plug insertion hole; wherein the case is provided with an installation part that holds the shutter such that it can rotate freely, and wherein the shutter mechanism can be installed from the outside to the installation part.