An optical module, comprising a printed wiring board and a multi-channel optical semiconductor element having a plurality of optical semiconductor elements, the printed wiring board comprising: a conductor plate that is divided into sections, comprising a lead section, a wiring section (Pw) and a mounting section; an insulating layer formed on and across the plurality of conductor plates; and a plurality of wiring patterns formed on the insulating layer opposite to the surface on which the conductor plate is formed; the lead section including one of the plurality of the separated conductor plates; and the wiring section including other one of the plurality of the separated conductor plates, the wiring section being electrically connected with the lead section; and the mounting section including still another one of the plurality of the separated conductor plates, and connected to a plurality of signal electrode strips (10i and a plurality of ground strips (10i) for electrical connection with the multi-channel optical semiconductor element having a plurality of optical semiconductor elements therewith, wherein at least one of the plurality of separated conductor plates is electrically connected with at least one of the plurality of wiring patterns through a via-hole, wherein the conductor plate of the mounting section is further separated into a predetermined number of signal conductor plate strips (10h) and a number of ground conductor plate strips (10h) corresponding to channels of the multi-channel optical semiconductor element to constitute the plurality of signal electrode strips together with corresponding electrode patterns, and the signal conductor plate strips (10h) and the ground conductor plate strips (10h) are electrically connected to the corresponding electrode patterns, respectively through a via-hole. a conductor plate that is divided into sections, comprising a lead section, a wiring section (Pw) and a mounting section; an insulating layer formed on and across the plurality of conductor plates; and a plurality of wiring patterns formed on the insulating layer opposite to the surface on which the conductor plate is formed; the lead section including one of the plurality of the separated conductor plates; and the wiring section including other one of the plurality of the separated conductor plates, the wiring section being electrically connected with the lead section; and the mounting section including still another one of the plurality of the separated conductor plates, and connected to a plurality of signal electrode strips (10i and a plurality of ground strips (10i) for electrical connection with the multi-channel optical semiconductor element having a plurality of optical semiconductor elements therewith, wherein at least one of the plurality of separated conductor plates is electrically connected with at least one of the plurality of wiring patterns through a via-hole, wherein the conductor plate of the mounting section is further separated into a predetermined number of signal conductor plate strips (10h) and a number of ground conductor plate strips (10h) corresponding to channels of the multi-channel optical semiconductor element to constitute the plurality of signal electrode strips together with corresponding electrode patterns, and the signal conductor plate strips (10h) and the ground conductor plate strips (10h) are electrically connected to the corresponding electrode patterns, respectively through a via-hole.