A gas processing apparatus is disclosed, that comprises a processing chamber that is airtightly structured, a gas delivery pipe connected to the processing chamber, a gas supply source for supplying gas to the processing chamber through the gas delivery pipe, a holding table for holding a workpiece loaded to the processing chamber, a shower member disposed at a gas outlet of the gas delivery pipe connected to the processing chamber, a spray plate structured as a partition wall of the shower member that faces the holding plate, the spray plate having a plurality of spray holes, and a baffle member disposed between the spray plate in the shower member and the gas outlet and having a plurality of through-holes formed perpendicular to the surface of the baffle member, wherein each of the through-holes of the baffle member has a first opening portion and a second opening portion facing the gas outlet, the second opening portion facing the spray plate, the opening area of the second opening portion being larger than the opening portion of the first opening portion. Thus, a gas processing apparatus and a gas processing method that allow gas to be uniformly supplied to the entire surface of a workpiece are provided. In addition, a baffle member for use with the gas processing apparatus and the gas processing method is provided.