The present invention addresses the problems of finding a treatment for minimizing the occurrence of condensation when subjecting the surface of a specific metal substrate having a thermal conductivity of 10 W/mK or more to flame treatment, and of continuously carrying out the treatment and flame treatment. In order to solve these problems, the present invention provides a pretreatment method forcoating or printing on the surface of a metal substrate, said pretreatment method including preheating the surface of a specific metal substrate having a thermal conductivity of 10 W/mK or more to 40DEG C or more prior to using a paint or ink to coat or print on the surface of the substrate, then continuously performing flame treatment on the surface of the substrate.