A supporting structure for ceramic tubes in a gas system in which a plurality of stages of tube support plates are provided in a substantially horizontal manner in a container, and ceramic tubes are supported with their axial lines being substantially vertical between the vertically adjacent tube support plates so that through holes formed in the tube support plates are communicated with the inner passages of the ceramic tubes, and metallic ring holders are respectively fitted to the outer periphery of the lower end portion of the tubes with interposed compacted layers while the metallic ring holders are in contact with the lower end faces of the tubes, and the ring holders are respectively in contact with and are supported by the tube support plates which are placed below the ring holders. Engaging means of the ceramic tubes to the tube support plates is also disclosed.