If, upon an occurrence of a jam, a sheet is detected by a sensor disposed downstream of a fixing portion or the leading end thereof has not reached this sensor and a coverage rate is high, the jam is judged to have occurred in the fixing portion. A number (x) of blank sheets to be passed is determined from a coverage rate of the entire sheet, and a cleaning mode is automatically executed if the automatic execution of the cleaning mode is selected, whereas a notification urging the input of an instruction as to whether or not to execute the cleaning mode is given if the automatic notification is selected. Therefore, toner adhered to the fixing portion can be simply and properly cleaned.