It is an object to provide a technique capable of using a single framer as a necessary framer and causing the framer to be shared among a plurality of transmission destinations and priorities when coping with a plurality of transmission destinations or priorities and a change in a bandwidth of a physical lane that is caused by a change in a modulation scheme or a change in the number of wavelengths.A multilane transmission device that allocates client signals based on a transmission destination or a priority, decides the number of virtual lanes necessary for transmission of the client signals allocated based on each transmission destination or each priority, allocates the client signals allocated based on each transmission destination or each priority to the virtual lanes whose number has been decided, and frames the client signals allocated to the virtual lanes as transport frames, multiplexes the virtual lanes into a physical lane, and transmits the framed transport frames by using the physical lane.