Apparatus (1) for changing a blade of a rotary die cutter, particularly for flexographic printing machines: a magnetic cylinder (3) configured to receive and support a die-cutting blade (5, 5′); a station (7) for inserting the blade (5, 5′) has a retention device (70) configured to retain the blade (5) in the insertion station; a guiding device (71) guides the blade (5, 5′) toward the magnetic cylinder (3); a station (9) for extracting the blade (5, 5′), has an extraction device (90) configured to remove the blade (5, 5′) from the magnetic cylinder (3).