A cutting device for a crosscut shredder is mounted in a housing, is driven by a motor through a transmission gear set and has two driving shafts, and two bracing leaves, multiple shredding blades and multiple partitions mounted on the driving shafts. The partitions are disposed between the shredding blades. The bracing leaves hold the driving shafts at middles of the driving shafts to structurally enhance the driving shafts so the driving shafts are not deformed easily. Therefore, the papers are shredded thoroughly, and the transmission gear set and the motor are able to operate appropriately and keep in good conditions. Moreover, the driving shafts have saved manufacturing costs and effective shredding capabilities.