To hold optimal a degree of consumption of a developing device and a transfer material conveyance belt and to form a successful image by appropriately conveying a transfer material irrespective of a size or a type of the transfer material.

When an image formation mode is for a monochrome image mode, whether the size of the transfer material is the right one with which the image is formed is determined even if a transfer conveyance belt 11a is kept apart from image writers 106C, 106Y, 106M. When the size of the transfer material is the one with which the image is formed even if the transfer conveyance belt 11a is kept apart, whether the transfer conveyance belt 11a is in a contacted state is determined. When the transfer conveyance belt is kept apart, an image forming apparatus starts an image forming operation according to the control mentioned above. When the transfer conveyance belt is in the contacted state, the transfer conveyance belt 11a is first moved to an apart position and the image forming operation is started according to the control mentioned above.