A film forming method forms a silicon film on a substrate placed on a turntable which rotates and passes through first and second process regions that are mutually separated along a circumferential direction inside a vacuum chamber that is settable to a first temperature at which Si—H bond dissociation can occur. A film forming process includes forming a molecular layer of SiH3 on the substrate, by supplying a Si2H6 gas that is set to a second temperature higher than the first temperature during a time period in which the substrate passes through the first process region, and forming a molecular layer of SiCl3 on the substrate having the molecular layer of SiH3 formed thereon while causing the Si—H bond dissociation in the molecular layer of SiH3, by supplying a gas including silicon and chlorine during a time period in which the substrate passes through the second process region.