A process for producing a polymer of a diallylalkylammonium halide which comprises polymerizing the diallylalkylammonium halide in the presence of a polymerization initiator in an aqueous solution containing a nitroxy radical. A first fluid line is connected to the fluid container so that it receives from the fluid container a first fluid stream substantially in the liquid state. The lifting slider and compression slider are provided with corresponding lifting rollers and compression rollers that engage the lid. The image data of each frame is corrected in accordance with the correction value.