A paper feeder includes a recording-media container, a width regulating member, and a locking mechanism. The recording-media container is attachable to and detachable from a body of an image forming apparatus. The recording-media container stores a recording medium. The width regulating member regulates a position in a widthwise direction of the recording medium stored in the recording-media container. The locking mechanism steplessly changes a movable range of the width regulating member in the widthwise direction. The width regulating member includes a lever configured to cooperate with the width regulating member to hold the locking mechanism so as to bring the locking mechanism into an unlocked state. The locking mechanism in a locked state restricts movement of the width regulating member in the widthwise direction, and regulates wobbling of the width regulating member in a direction orthogonal to the widthwise direction.