An image forming apparatus includes a paper reading section, a similarity judgment section, and a control section. Between a downstream side in a paper conveyance direction of the paper feed section and a position where image formation is performed, the paper reading section reads an existing image already formed on a surface opposite to a formation surface of a new image newly formed on paper by an image formation section. Based on image data of the new image and image data of the existing image obtained by the image formation section, the similarity judgment section judges similarity between the both images. The control section, upon judging that the similarity is high, causes a pattern image to be formed on a surface of the paper where the existing image is formed, and upon judging that the similarity is not high, does not cause the pattern image to be formed.

An image forming apparatus includes a paper reading section, a similarity judgment section, and a control section. Between a downstream side in a paper conveyance direction of the paper feed section and a position where image formation is performed, the paper reading section reads an existing image already formed on a surface opposite to a formation surface of a new image newly formed on paper by an image formation section. Based on image data of the new image and image data of the existing image obtained by the image formation section, the similarity judgment section judges similarity between the both images. The control section, upon judging that the similarity is high, causes a pattern image to be formed on a surface of the paper where the existing image is formed, and upon judging that the similarity is not high, does not cause the pattern image to be formed.

A sheet conveyer to shift a sheet at one side of the sheet conveyer in a widthwise direction is provided. The sheet conveyer includes a pair of rollers, a regulative guide arranged at a position closer to the one side than the pair of rollers in the widthwise direction, a first guide arranged at a position upstream from the pair of rollers with regard to a conveying direction to contact a first area on a first face of the sheet at a position closer to the one side in the widthwise direction than a widthwise center of the sheet, and a second guide arranged at a position upstream from the pair of rollers with regard to the conveying direction to contact a second area on a second face of the sheet. The second guide partly overlaps the first guide in a direction of height.

A sheet conveyer to shift a sheet at one side of the sheet conveyer in a widthwise direction is provided. The sheet conveyer includes a pair of rollers, a regulative guide arranged at a position closer to the one side than the pair of rollers in the widthwise direction, a first guide arranged at a position upstream from the pair of rollers with regard to a conveying direction to contact a first area on a first face of the sheet at a position closer to the one side in the widthwise direction than a widthwise center of the sheet, and a second guide arranged at a position upstream from the pair of rollers with regard to the conveying direction to contact a second area on a second face of the sheet. The second guide partly overlaps the first guide in a direction of height.