Provided is an optical submodule which includes an optical transmission/reception module that optically couples an optical transmission signal and an optical reception signal into one optical fiber and a flexible printed circuit board (FPCB) mounted on the optical transmission/reception module that functions as an electrical signal interface with a main board, and an electrical signal line of an optical transmission channel for the optical transmission signal and an electrical signal line of an optical reception channel for the optical reception signal may be deployed on different sides of the FPCB.