A size storing unit stores a size of a ring member for binding stacked sheets. A range determining unit determines whether a thickness represented by input thickness information is larger than a minimum total thickness of sheets allowed to be bound with a ring member having the stored size and equal to or smaller than a maximum total thickness of sheets that can be bound with the ring member. When it is determined that the thickness represented by the thickness information is equal to or smaller than the minimum total thickness or larger than the maximum total thickness, a setting unit sets the size stored in the size storing unit to a different size.