To provide an image processor capable of more efficiently performing image processing in a transition period required until shifting to a state where an image output device can stably operate after turning on a power source of an image forming apparatus than the conventional one, an image forming system and an image processing program.

The image processor includes an implementation controller 32a which allows a plurality of DRPs (dynamic reconfigurable processors) 61 to 68 to implement first image processing concerning paginating and second image processing different from the first image processing. The implementation controller 32a allows all the DRPs 61 to 68 to implement the second image processing, when a printing job is input in the transition period required until shifting to the state where the image output device 1a can stably operate after turning on the power source of the image forming apparatus 1.