1. An image forming apparatus, comprising: a document image acquiring portion that acquires a document image; an integration pattern determining portion that makes settings relating to integration for each integrated document image when plural document images are integrated into a recording sheet as integrated document images and thereby determines an integration pattern of the integrated document images for the recording sheet; a page number setting portion that sets a page number of the plural document images upon receipt of the instruction about the page number of the plural document images input by the user; an integrated document image generating portion that generates the integrated document images corresponding to the integration pattern from document images acquired by the document image acquiring portion according to the integration pattern determined by the integration pattern determining portion; a display portion that displays a setting screen used to make settings relating to the integration of the acquired document images and a recording sheet image representing the recording sheet, and accepts an operation instruction input by a user; a switching portion that displays plural recording sheet images each including a specific number of the integrated document images on the setting screen by switching in the unit of pages in response to the acceptance of the operation instruction input by the user; and a print portion that prints the integrated document images generated by the integrated document image generating portion onto the recording sheet in the integration pattern, wherein the integration pattern determining portion prepares the recording sheet images distributed in a plurality of pages according to information relating to the page number set by the page number setting portion, makes settings as to movement, rotation and scaling up or down of the respective integrated document images for the recording sheet images in response to the operation instruction input by the user on the setting screen, and determines an entire integration pattern representing an integration pattern of the integrated document images for the recording sheet images by setting an alignment sequence of the document images for the respective integrated document images, the switching portion displays the recording sheet images distributed in the plurality of pages on the setting screen by switching in the unit of pages in response to the operation instruction input by the user in determining the entire integration pattern, the integrated document image generating portion generates the integrated document images corresponding to the entire integration pattern from the document images acquired by the document image acquiring portion according to the entire integration pattern, the integration pattern determining portion is further furnished with a drag processing function of performing at least one of movement, rotation, and scaling up or down processing of the respective integrated document images in response to an instruction input by a dragging operation by the user on the setting screen, the display portion is provided with an integration pattern image display region that displays the integration pattern, and a button document image display region that displays a button document image schematically displaying a document, the display portion displaying information relating to an orientation of a document together with the button document image, with the information relating to the orientation being attached on the button document image itself, the integration pattern determining portion accepts an operation of moving the button document image to the integration pattern image display region by the dragging operation, and the display portion displays the moved button document image as an integrated document image in the integration pattern image display region.