In a pipeline process operation including a branching process unit 25 as one of process modules, this branching process unit 25 is provided with an input management unit 251 for managing an input condition, a branching information management unit 252 for managing information as to branching destinations, a buffer unit 253 whose upper storage limit can be designated, and a branching control unit 254 for controlling an entire branching process unit. The branching process unit 25 may execute an arbitrary number of branching process operations without having such a buffer for an entire image.