A trimmer configured for trimming a bound material which has a book block and a cover attached to the book block, the cover having flap portions adjacent to the fore-edge portion of the bound material, the trimmer comprising a trim unit including: a trim cutter configured for trimming the bound material; a blade receiving portion configured for receiving an edge of the trim cutter; a base portion and a pressure portion configured for nipping and positioning the bound material; and a pair of guide portions (60,61) arranged for movement in a direction close to or away from the bound material including an upper guide portion attached to the pressure portion and a lower guide portion attached to the base portion; and a pressure portion driving mechanism configured for reciprocating the pressure portion between a non-pressing position and a pressing position, the non-pressing position being a position where the pressure portion is spaced from the bound material, the pressing position being a position where the bound material is pressed against the base portion; and the trimmer further comprising a table configured for positioning the bound material placed thereon; and a table unit configured for rotating the table in such a manner that the bound material is rotated to each of top, bottom, and fore-edge trimming positions; the trimmer further comprising a driving mechanism configured for moving the trim unit and/or the table unit between a trimming position and a stand-by position, the trimming position being a position at which the trim cutter is pushed against the blade receiving portion, the stand-by position being a position at which the trim cutter is spaced from the bound material; wherein the pressure portion driving mechanism is configured for moving the upper guide portion and the pressure portion from the non-pressing position to a peeling up position while the trim unit is stopped at the stand-by position, the peeling up position being disposed between the non-pressing position and the pressing position, such that the upper guide portion being contacted with the book block when the upper guide portion is disposed on the peeling up position; and wherein the trimmer is further configured such that the upper guide portion and the lower guide portion are inserted between the book block and the cover so as to peel the cover together with the flap portions up when the driving mechanism causes the trim unit and/or the table unit to move from the stand-by position to the trimming position. a trim cutter configured for trimming the bound material; a blade receiving portion configured for receiving an edge of the trim cutter; a base portion and a pressure portion configured for nipping and positioning the bound material; and a pair of guide portions (60,61) arranged for movement in a direction close to or away from the bound material including an upper guide portion attached to the pressure portion and a lower guide portion attached to the base portion; and a pressure portion driving mechanism configured for reciprocating the pressure portion between a non-pressing position and a pressing position, the non-pressing position being a position where the pressure portion is spaced from the bound material, the pressing position being a position where the bound material is pressed against the base portion; and the trimmer further comprising a table configured for positioning the bound material placed thereon; and a table unit configured for rotating the table in such a manner that the bound material is rotated to each of top, bottom, and fore-edge trimming positions; the trimmer further comprising a driving mechanism configured for moving the trim unit and/or the table unit between a trimming position and a stand-by position, the trimming position being a position at which the trim cutter is pushed against the blade receiving portion, the stand-by position being a position at which the trim cutter is spaced from the bound material; wherein the pressure portion driving mechanism is configured for moving the upper guide portion and the pressure portion from the non-pressing position to a peeling up position while the trim unit is stopped at the stand-by position, the peeling up position being disposed between the non-pressing position and the pressing position, such that the upper guide portion being contacted with the book block when the upper guide portion is disposed on the peeling up position; and wherein the trimmer is further configured such that the upper guide portion and the lower guide portion are inserted between the book block and the cover so as to peel the cover together with the flap portions up when the driving mechanism causes the trim unit and/or the table unit to move from the stand-by position to the trimming position.