A feeder unit to feed sheets is provided. The feeder unit includes a main frame, being swingably supported at a pivotal end by a first shaft, and arranged to extend from the first shaft toward an upper level of a tray, a rotary member, which is rotatably supported, and is arranged to come in contact with a topmost surface of the sheets, a pair of opposing walls, formed in the main frame, a secondary frame, having a pair of supporting walls which come to face the opposing walls, a gear train to transmit rotation force to the rotary member, a positioning system to situate the secondary frame in a predetermined position, and a detachment restricting system to restrict the secondary frame from being detached from the main frame. The secondary frame is situated in the predetermined position when the rotary member rotates in a direction to feed the sheets.