The present invention provides an optical module with an improved temperature condition surrounding an opto-electronic device. The optical module of the present invention comprises an optical sub-assembly including an opto-electronic device, a first circuit board electrically connected to the optical sub-assembly, an electronic device mounted on the first circuit board, a lower housing for mounting the first circuit board, an upper housing for covering the circuit board and electronic device, and a metal cover for covering the upper housing. Constructed in the optical module are a first heat-dissipating path for dissipating heat from the electronic device to the cover via the upper housing, and a second heat-dissipating path, different from the first heat-dissipating path, for dissipating heat from the optical sub-assembly to the cover by way of the upper housing.