To provide a method of determining the direction of a substrate, capable of improving throughput of a product such as a mounting substrate.

The method of determining the direction of a substrate includes an information acquiring step S100 for acquiring NC data indicating a mounting target region in a substrate to be treated as a target of component mounting by a component mounter; a step S102 of calculating the number of carrying times, for calculating the number of times of carrying a substrate required for executing component mounting for all the mounting target regions by the component mounter on the basis of the positional relation between the mounting target region and a mountable range indicated by the NC data when the substrate is carried along a direction to the component mounter for each direction of the substrate; and determining steps S106 and S110 for determining the direction having the minimum number of carrying times as the direction of the substrate to be set.