An optical module includes a package, a substrate, a lead pin, and a ground pattern. The substrate is accommodated in the package, includes a signal line pattern that transmits an electric signal, extends toward a side wall of the package beyond an end of the signal line pattern, and has a through hole between the end of the signal line pattern and the side wall of the package. The lead pin is inserted into the through hole in the substrate and inputs the electric signal to the end of the signal line pattern. The ground pattern is provided in at least a part of regions surrounding the through hole on the substrate.