The present invention provides an image forming apparatus and a malfunction diagnosis method of the image forming apparatus. The image forming apparatus stores a diagnosis target of a malfunction in association with a diagnostic item corresponding to the diagnosis target, and in a case where an abnormality is detected, the apparatus specifies the diagnosis target corresponding to the abnormality, executes a malfunction diagnosis process in accordance with the stored diagnostic item in association with the specified diagnosis target, and displays information regarding a malfunction parts determined to be a malfunction by the malfunction diagnosis process. The apparatus executes a malfunction diagnosis processes of a different type depending on whether or not a sheet remaining in the image forming apparatus is detected.