A poly-silicon film formation method for forming a poly-silicon film doped with phosphorous or boron includes heating a target substrate placed in a vacuum atmosphere inside a reaction container, and supplying into the reaction container a silicon film formation gas, a doping gas for doping a film with phosphorous or boron, and a grain size adjusting gas containing a component to retard columnar crystal formation from a poly-silicon crystal and to promote miniaturization of the poly-silicon crystal, thereby depositing a silicon film doped with phosphorous or boron on the target substrate.