A plug in which the base end portions of an image guide comprise an image guide fiber and an image guide rod. A light guide comprising a light guide fiber and a light guide rod are fixed to a plug main body in a parallel state. The plug and a socket can be connected. The diameter of a position-aligning hole portion into which the base end of the image guide rod is inserted is set to be substantially the same as the outer diameter of the image guide rod, while the diameter of a position-aligning hole portion into which the base end of the light guide rod is inserted is set to be greater than the outer diameter of the light guide rod.
