PURPOSE: To improve the service life of a plug, and to prevent the on the inside surface of a tube by supplying effectively a lubricant.

CONSTITUTION: Salt is thrown into the inside of a hollow tube stock T heated to a prescribed temperature, the salt is melted, a state that the inner wall of a tube is wet with molten salt is formed, and thereafter, a plug 12 is inserted into the hollow tube stock T, and plug rolling of a first pass is executed. Rolling of a first pass is executed by injecting graphite to a rolling part Ta from a graphite injection hole 22, ad also, while injecting salt to the inner wall of the tube after rolling from a salt injection hole 24. The graphite adheres uniformly and surely by an action of molten salt, therefore, a sufficient lubricating performance can be displayed. After rolling of a first pass is finished, the hollow tube stock T is returned to the entry, and rolling of a second pass (final) is executed, while injecting the graphite. At the time of rolling of a second pass, as well, the lubricating performance of the graphite can be displayed enough in the same way.