A paper binding device comprises: a pair of binding members that has a pair of teeth portions, and presses to bind a bundle of paper sheets; a moving unit that causes one of the pair of binding members to move along with the other of the pair of binding members between a binding position at which the bundle of paper sheets is bound and a retracted position; a separating unit that moves coordinating with movement of the one of the pair of binding members, and when the one of the pair of binding members moves from the binding position to the retracted position, that contacts with the bundle of the paper sheets and causes the bundle of paper sheets to separate from the one of the pair of binding members; and a restricting member that stops the separating unit at a restricting position between the binding position and the retracted position, when the one of the pair of the binding members moves from the binding position to the retracted position.