There is provided a method of forming a film on a surface to be processed of a workpiece, the method including: accommodating the workpiece with a single-crystallized substance formed on the surface to be processed, into a processing chamber; supplying a crystallization suppressing process gas into the processing chamber such that a crystallization of the single-crystallized substance formed on the surface to be processed is suppressed; and supplying a source gas into the processing chamber to form an amorphous film on the surface to be processed of the workpiece.