A paper binder configured to punch a hole in a plurality of layered paper sheets to cut off part of the paper sheets and form ligulate strips and form incisions near the strips and insert the strips into the incisions to bind the paper sheets, comprising: a base; a support base erected on the base; a handle that is connected to the support base via a rotation shaft and that is rotatable about the rotation shaft; characterised by a pair of punch blades that protrude from the base toward the handle and punch holes; a pair of incising blades that protrude from the base toward the handle and form the incision; a pair of projections that are rotated together with the rotation of the handle and press against the formed strips to fold the strips toward the paper sheets; a mounting base that is arranged between the base and the handle, provided with through-holes through which the edge parts toward the projection direction of the projections, the punch blades, and the incising blades are able to pass, on which the paper sheets are mounted; a pressing portion that is arranged at a position enclosed by the handle and the mounting base, that is capable of receiving each of the edge parts passing through the through-holes, that includes reception holes in the interior in which the projections are able to rotate, that is configured so that the vicinity of the through-holes of the mounting base are visible from the side of the handle through at least the reception holes and their surroundings, and that pinches the paper sheets together with the mounting base; a window portion provided on the handle at a part including a region overlapping with at least the reception holes of the pressing portion; and a movement mechanism that brings closely the relative positions of the pressing portion and the mounting base depending on the handle rotates, and moves the mounting base toward the base together with the pressing portion, wherein as a result of the pressing portion and the mounting base being brought closely by the movement mechanism, the paper sheets on the mounting base are pinched, and by moving the pressing portion and the mounting base toward the base while pinching the paper sheets, the edge parts of the punch blades and the incising blades are pressed against the paper sheets to form the strips and the incision. a base; a support base erected on the base; a handle that is connected to the support base via a rotation shaft and that is rotatable about the rotation shaft; characterised by a pair of punch blades that protrude from the base toward the handle and punch holes; a pair of incising blades that protrude from the base toward the handle and form the incision; a pair of projections that are rotated together with the rotation of the handle and press against the formed strips to fold the strips toward the paper sheets; a mounting base that is arranged between the base and the handle, provided with through-holes through which the edge parts toward the projection direction of the projections, the punch blades, and the incising blades are able to pass, on which the paper sheets are mounted; a pressing portion that is arranged at a position enclosed by the handle and the mounting base, that is capable of receiving each of the edge parts passing through the through-holes, that includes reception holes in the interior in which the projections are able to rotate, that is configured so that the vicinity of the through-holes of the mounting base are visible from the side of the handle through at least the reception holes and their surroundings, and that pinches the paper sheets together with the mounting base; a window portion provided on the handle at a part including a region overlapping with at least the reception holes of the pressing portion; and a movement mechanism that brings closely the relative positions of the pressing portion and the mounting base depending on the handle rotates, and moves the mounting base toward the base together with the pressing portion, wherein as a result of the pressing portion and the mounting base being brought closely by the movement mechanism, the paper sheets on the mounting base are pinched, and by moving the pressing portion and the mounting base toward the base while pinching the paper sheets, the edge parts of the punch blades and the incising blades are pressed against the paper sheets to form the strips and the incision.