1. A method of forming a detection mark from a line pattern formed on a substrate, comprising: a first step of deciding a first region for forming the detection mark on the substrate, and a second region which surrounds the first region and in which formation of the detection mark is forbidden; and a second step of projecting, onto the substrate by a projection optical system, patterns including a first cut pattern for partially cutting the line pattern in the first region to form a plurality of mark elements, and a removal pattern for removing the line pattern in the second region, and forming the detection mark including the plurality of mark elements.