In a laser printer using a plurality of laser scan units, a laser scan unit is capable of manually adjusting a plurality of laser beams to be parallel. The laser scan unit assembly includes a laser scan unit having a window on a front surface through which a laser beam is emitted, a hinge portion provided at one side of the laser scan unit to pivotably dispose the laser scan unit on the body, and an adjusting portion provided on the side of the laser scan unit opposite from the hinge portion, to adjust an amount the laser scan unit pivots. The body has a hinge supporting portion provided thereon to support rotation of the hinge portion. The hinge portion is formed as a hinge shaft and the hinge supporting portion is formed as a groove to support the hinge shaft. The adjusting portion includes a first adjusting unit which is an inclined surface, and a second adjusting unit which is a screw and is provided on the body.