There is provided an optical module including an optical subassembly including an optical element, a printed circuit board, and a connection substrate. The connection substrate includes a first connection portion connected to a first signal line conductor strip disposed on a first surface and a first ground conductor layer disposed on a second surface. The first connection portion includes a first signal line pad portion, a first ground pad portion, both disposed on the first surface, a second signal line pad portion disposed, and a second ground pad portion, both disposed on the second surface. In the connection substrate, a distance between the first signal line pad portion and the first ground pad portion in a first region is narrower than that in a second region farther from an inner end portion on the gap portion side than the first region in plan view.