A rack mount apparatus is provided in an optical transmission apparatus. The rack mount apparatus includes a rack, a shelf mounted in the rack and a cross-sectional L-shaped Panel installed in the rack under a device to be rotatable so as to take an opened position and a closed position. This enables not only an easy and reliable connection of an interface cable in the rack mount apparatus without imposing a stress thereon but also a flexible determination or change of a connection position of the interface cable and even considerable improvement of the working efficiency.