An image forming apparatus which has an image signal generator for generating an image signal, an image forming unit for forming an image on a recording medium based on the generated image signal, a feeding unit for feeding the medium to the image forming unit, and a controller for outputting different commands to the image forming unit to control the image forming unit. The feeding unit performs spare paper feeding of the medium to a predetermined position before the generator is set in an image signal output enable state and feeds the medium from the predetermined position to the image forming unit after the generator is set in the image signal output enable state. The image forming unit validates a specific command of the different commands when the specific command is received during at least a spare paper feed period from start of spare paper feeding of the recording medium to start of paper feeding from the predetermined position, thereby maximizing the function of the image forming apparatus.