The present disclosure provides a novel notebook system in which stacks of one-side-bound inner paper sheets are replaced, wherein a plurality of pockets are formed at a plurality of positions in an inner face of an outermost cover sheet, a first or last paper sheet of the stack of one-side-bound inner paper sheets is removably inserted into the pocket selected by the user, and, therefore, the handwriting direction or position may be freely changed according to the user's selection. According to the present disclosure, the user can freely change the position of the stack of one-side-bound inner paper sheets, and thus can make notes or handwriting in a convenient way. When the stack of one-side-bound inner paper sheets are completely used, the stack may be replaced with a new stack of one-side-bound inner paper sheets, which can save money and waste material.