Provided are an on-board update device, an update process method, and an update process program capable of appropriately updating a plurality of on-board devices installed in a vehicle if a plurality of update processes are provided through different paths. The on-board update device according to this embodiment performs communication via external communication units, and includes an execution determination unit configured to determine, if different update programs are respectively received from different external devices via a plurality of external communication units, based on version information of the update programs, whether or not it is possible to perform an update process using each update program, and, if the execution determination unit has determined that it is possible to perform update processes with regard to a plurality of update programs, an update process unit performs update processes using the plurality of update programs in parallel.