a semiconductor device manufacturing method comprises a process of forming a film on each of multiple substrates arrayed in a processing chamber by a thermal cvd method by supplying a film forming gas into the processing chamber while heating the interior of the processing chamber , wherein in the film forming process , a cycle is performed one time or multiple times with one cycle including a step of flowing the film forming gas from one end towards the other end along the substrate array direction , and a step of flowing the film forming gas from the other end towards the one end along the substrate array direction , without forming temperature gradient along the substrate array direction in the processing chamber .