An optical data link 20 comprises a mounting member 22, an optical element assembly 24, a circuit board 26, and a spacer 32. The PGA substrate 22 has a substrate 22a and a plurality of electrically conductive pins 22b. The circuit board 26 has a pair of surfaces. Electronic components 34a to 34e are mounted on the pair of surfaces. The optical element assembly 24 includes a semiconductor optical element 24f. The semiconductor optical element 24f is connected to an electrically conductive layer on the circuit board 26. The spacer 32 functions so as to distance the circuit board 26 from the PGA substrate 22. Since the circuit board 26 is distanced from the PGA substrate 22, the electronic components 34a to 34e can be mounted on both surfaces of the circuit board 22.