An image forming apparatus receives raster image data transferred from an external device and forms an image on the basis of the received raster image data. The apparatus includes a processor that controls a transfer of the raster image data from the external device, a first memory connected to the processor through a first bus is used as a working area of the processor, a second memory that stores the raster image data, a memory control unit connected to the second memory through a second bus controls an operation of writing and reading the raster image data in and from the second memory, a printer engine that forms an image on the basis of the raster image data, and an engine control unit that reads the raster image data from the second memory through the memory control unit and supplies the printer engine with the read raster image data.