The invention disclose an image forming apparatus provided with display device, displaying method and screen generating method. The MFP includes an EEPROM storing display screens, and a display control portion to read a display screen for display on a display portion. When a first area in the display screen includes a variable display item for which an arbitrary number of data pieces are displayed, the display control portion acquires the number of data pieces to be displayed therefor, changes the size of a field for the variable display item based on the acquired number of data pieces, determines the size of a second area based on the size of the first area after the size change of the variable display item field and the size of the display area of the display portion, and modifies the read display screen to a display screen having the first area after the size change of the variable display item field and the second area of the determined size arranged therein.