SG12A tube reducing machine is using the high-quality gear motor as its power, which is sent to the gear case through the double spindle. The cross transmission shaft is connected with the roller seat. Using rolling reducing method, tubes after reduced with smooth surface, roundness ±0.05mm, straightness accuracy less than 0.5mm within 1000mm. The roller head structure is universal with SG12B, which can be separated with the machine frame and to be changed as a whole. One motion seat can wear several roller seat assemblies of different standards to achieve quick changing of the standard to fit producing need of different tubes.