To efficiently cool an IC chip and a transmission module disposed on the same substrate, amounting structure of transmission module of the present invention includes a motherboard, a package substrate mounted on the motherboard, an IC chip and a plurality of connectors disposed on amounting surface of the package substrate, a plurality of transmission modules connected to the plurality of connectors, and module cooling members having a plurality of slits provided along an connector array direction. The connectors are disposed inside the slits of module cooling members, and the transmission modules can be connected to and disconnected from the connectors disposed through the slits. The transmission modules connected to the connectors are in contact with inside surfaces of the slits and thermally connected to the cooling members.