PROBLEM TO BE SOLVED: To provide a substrate reuse method that enables a residue remaining on a surface of a substrate from which CNT has been peeled to be easily removed and that enables the substrate to be reused for a new CNT synthesis.SOLUTION: The substrate reuse method is configured to reuse a substrate obtained through a step of synthesizing a CNT using a substrate in which a catalyst layer made of catalyst metal is deposited on a smooth base plate and a step of peeling the CNT from the substrate surface. The method includes a step of bringing the substrate processed in the above steps into a high temperature furnace 2, a step of introducing a first cleaning gas containing oxygen gas into the high temperature furnace 2 and then heating the substrate to remove compounds containing carbon on the substrate surface, and a step of introducing a second cleaning gas containing a chlorine-based gas into the high temperature furnace 2 and then heating the substrate to remove compounds containing metal on the su
