An image forming apparatus, as a displaying device, displays the 2nd printing page out of a plurality of printing pages on an operation panel when the 1st to 10th images were allocated to each of the printing pages. The image forming apparatus maintains an allocation state of the 1st printing page anterior to the 2nd printing page and changes an allocation state of at least one of images corresponds to the contact points with the operation panel, when the image forming apparatus receives a gesture operation moves the contact points. The starting points of the contact points are in the 2nd printing page displayed on the operation panel.