A trimmer for trimming a bound material, including: a table on which the bound material is to be placed; a pressing unit fixing the bound material on the table; a trimming mechanism having a single trimming blade and being configured for moving the trimming blade between a trimming position and a non-trimming position so as to trim the bound material; a rotation mechanism configured for rotating the table; a rotation control unit operatively connected to the rotation mechanism so as to rotate the table in such a way that a predetermined trimming line is positioned parallel to a longitudinal direction of the trimming blade, the predetermined trimming line being set for the edge portion of the bound material; a moving mechanism configured for moving the table or the trimming mechanism in a direction perpendicular to the longitudinal direction of the trimming blade; and a movement control unit operatively connected to the moving mechanism so as to move the table or the trimming mechanism in such a way that the trimming line and the trimming position are aligned with each other, characterized in that the rotation control unit is operatively connected to the rotation mechanism further so as to rotate the table in such a way that a predetermined trimming line is positioned parallel to the longitudinal direction of the trimming blade, the predetermined trimming line being set for a corner portion of the bound material; and the movement control unit is operatively connected to the moving mechanism further so as to move the table or the trimming mechanism in such a way that the trimming line and the trimming position are aligned with each other. a table on which the bound material is to be placed; a pressing unit fixing the bound material on the table; a trimming mechanism having a single trimming blade and being configured for moving the trimming blade between a trimming position and a non-trimming position so as to trim the bound material; a rotation mechanism configured for rotating the table; a rotation control unit operatively connected to the rotation mechanism so as to rotate the table in such a way that a predetermined trimming line is positioned parallel to a longitudinal direction of the trimming blade, the predetermined trimming line being set for the edge portion of the bound material; a moving mechanism configured for moving the table or the trimming mechanism in a direction perpendicular to the longitudinal direction of the trimming blade; and a movement control unit operatively connected to the moving mechanism so as to move the table or the trimming mechanism in such a way that the trimming line and the trimming position are aligned with each other, characterized in that the rotation control unit is operatively connected to the rotation mechanism further so as to rotate the table in such a way that a predetermined trimming line is positioned parallel to the longitudinal direction of the trimming blade, the predetermined trimming line being set for a corner portion of the bound material; and the movement control unit is operatively connected to the moving mechanism further so as to move the table or the trimming mechanism in such a way that the trimming line and the trimming position are aligned with each other.