Provided is a technique of forming an aluminum film that has high flatness and less cavities. Step S11 is forming a first film having a thickness that is equal to or greater than 0.1 μm and less than 1 μm, by sputtering a material onto a substrate. Step S12 is reflowing the first film by heating the first film. Step S13 is forming a second film by sputtering the material onto the first film that has been reflowed. Step S14 is reflowing the second film by heating the second film. Step S15 is forming a third film by sputtering the material onto the second film that has been reflowed. Step S16 is reflowing the third film by heating the third film.