To provide a cutting method that can cut a substrate part 1 of a heat sink material M accurately and quickly to a length required for a heat sink m as a product.

A stopper 6 is used to abut the root portion of a leading fin 2a in a leading fin group 3 in a reference position beyond a cutting position CP from the forward side thereof in a heat sink material feed direction and thus limit a leading fin-side reference length α of the substrate part 1. A pusher 7 is used to push the heat sink material M so that the stopper 6 abuts the root portion of the leading fin 2a. With the stopper 6 first positioned in the reference position, the pusher 7 causes the stopper 6 to abut the root portion of the leading fin 2a of the leading fin group 3, and the leading fin 2a side is cut away, after which the heat sink material M is fed by a given length L and a trailing fin 2b side is cut off. The process is thereafter repeated.