A seamless tube is manufactured while effectively suppressing the occurrence of carburization in the seamless tube without interfering with operations.A seamless tube is manufactured by a step of washing at least a portion of a conveyor installed in a conveying step of a mandrel bar B which is situated from a lubricant applying device 7 to the entrance of a mandrel mill 8, a step of washing, on the upstream side of the lubricant applying device 7, a mandrel bar B which was used for elongation rolling, and a step of applying a non-graphite-based lubricant to the mandrel bar B with the lubricant applying device 7, wherein the conveyor and the mandrel bar B are each washed such that the amount of graphite C2 (g/m2) adhering to the surface of the mandrel bar B before it is provided to elongation rolling and the amount of carbon C1 (g/m2) contained in the organic binder of the applied lubricant satisfy Equation 1: 0.08×C1+0.05×C2≦3 and Equation 2: 3≦C1+C2≦50.