An image forming processing circuit and an image forming apparatus having a clock stop function of the invention perform, in an image forming processing process, supply of a clock for processing only in a period in which the clock is required and stop the supply of the clock for processing in a period in which the clock for processing is not required. An ASIC itself realizes a low power consumption function (a clock stop function) without requiring control from a CPU or the like as in the conventional sleep function. Thus, it is possible to effectively reduce power consumption of the ASIC compared with that in the past.