In an image forming apparatus, in a case that a connected numerical key unit is a dedicated numerical key unit including a numerical key portion for executing, as predetermined processing, numerical value input processing for inputting information on a numerical value and including an operation key portion and a setting key portion for executing, as predetermined processing, another input processing for inputting information on an operation of the image forming apparatus other than the numerical value input processing (step S12; YES), a controller executes the predetermined processing in a case that either of the respective key portions is operated (step S13). On the other hand, in a case that the connected numerical key unit is a general-purpose numerical key unit different from the dedicated numerical key unit (step S1; NO), the controller executes the predetermined processing only in a case that the numerical key portion is operated (step S14).