PURPOSE: To reduce the cast of members and the man-hour of attachment for fixing an optical transmission module and an optical reception module to a case and to make a device light-weight and small-sized by fitting and fixing groove parts, which are in respective holder parts of the optical transmission module and the optical reception module, to notched parts provided in the case.

CONSTITUTION: In the optical interface module provided with a transmission/ reception function in a node system used for optical communication, approximately semicircular notched parts 9a and 9b are provided in a case 9, and a circular groove part 10a of an optical reception module 10 is fitted and fixed to the notched part 9a of the case 9. A circular groove part 11a of an optical transmission module 11 is fitted and fixed to the notched part 9b of the case 9. Thus, the cost of members and the man-hour of attachment for fixing to the case 9 are reduced, and the thickness of the case 9 is reduced to reduce the weight to a half, and further, the attachment gap between modules 10 and 11 is narrowed to miniaturize the device.