An optical module includes: a plurality of leads arranged in at least two lines, at least portions of the plurality of the leads being mounted on a circuit board; an optical semiconductor for emitting or receiving an optical signal; and a circuit portion connected to the optical semiconductor, for transmitting a pair of differential signals to or receiving a pair of differential signals from the circuit board through a pair of differential signal leads among the plurality of the leads. The pair of the differential signal leads are provided adjacent and in parallel to each other in one of the at least two lines.