PURPOSE: To transversely move a sheet to a register roller device positioned just before an image transfer section in an image forming device, in such a condition that the leading end part of the sheet is nipped, and to allow the aligning mechanism to surely align the sheet.

CONSTITUTION: A roller device composed of a register roller device 10 and a preregister roller device 20 and a gate member 6 are provided to a frame 2 of a sheet aligning device 1 which is provided to a toner image forming section such as a photosensitive drum in an image forming device, just before an image transfer part. In the above-mentioned sheet aligning device, a mechanism 30 for moving the register roller device, perpendicular to a sheet conveying direction, is provided so as to transversely move the register roller device in accordance with detection data for the side part of a sheet by a sheet sensor. Further, an engaging member 31 is provided in order to position a drive roller 11 and a pinch roller opposed to the roller 11 in the register roller device, thereby the positioning of the upper and lower rollers can be easily made during closing of the upper frame of the image forming device from a swing-up opening condition.