To provide a slitter device capable of preventing peeling or the like during cutting of a transfer ribbon or the like, and to provide a slitter machining method.

The slitter device for cutting a long base material with a prescribed width includes: unwinding means for unwinding a long base material having a transfer layer formed on one surface; a slitter for cutting the long base material with a prescribed width; a conveyance roll for maintaining tension at a contact between the long base material and the slitter; an inversion roll for contact with the slitter on the transfer layer forming surface of the long base material; and winding means for winding the cut long base material. The slitter machining method is characterized in that the slitter device conveys the long base material having the transfer layer formed on one surface while maintaining tension between two conveyance rolls, and bringing the slitter for cutting the roll base material with a prescribed width to cut from the surface of the roll base material, where the transfer layer is formed.