1. An image forming apparatus including a plurality of processors which perform interpretation processing of rendering commands and image forming processing, comprising: an accelerating processing determination unit which determines a process that allows accelerating processing, which is defined in advance, of processes included in the rendering commands; a processing cost determination unit which compares a processing cost calculated when the accelerating processing defined for each type of process is applied to the process which is determined by the accelerating processing determination unit to allow the accelerating processing with a processing cost calculated when the accelerating processing is not applied, and determines whether or not to apply the accelerating processing; a processing unit generation determination unit which determines based on the determination result of the processing cost determination unit whether or not to generate a new processing unit required for the plurality of processors to process the process determined to allow the accelerating processing; a generation unit which generates the process determined to allow the accelerating processing, in the new processing unit based on the determination result of the processing unit generation determination unit; and an accelerating processing execution unit which controls the plurality of processors to execute the process in the new processing unit generated by the generation unit, wherein the accelerating processing execution unit controls the processor different from the processor which performs the image forming processing to execute at least a part of the new processing unit.