In optical module 1a, substrate 3 has first and second regions 3a, 3b and first and second optical waveguides 3c, 3d. First and second regions 3a, 3b are arranged along a predetermined plane. First and second optical waveguides 3d, are provided in the first region 3a and extend in a direction of a predetermined axis. Semiconductor light emitting device 7 includes a semiconductor light emitting element 7a optically coupled to first optical waveguide 3c and provided in second region 3e. Semiconductor driving element 9 is electrically connected to semiconductor light emitting element 7a. Semiconductor driving element 9 is mounted on mount member 13. Optical element 15a reflects a part of incident light and transmits a part of the incident light, and semiconductor light receiving device 17 includes a light receiving element 17a provided in first region 3a so as to be optically coupled to optical element 15a.