PURPOSE: To manufacture a finned tube having no excess projection by passing a tube stock of deviated thickness, in which the thickness of a part passing a roller gap set to zero is thinner than the thickness of other circular tubes, through a coliber formed from a roller.

CONSTITUTION: Four coliber rollers 11 are provided on the periphery in such a state that each rotational axis 12 is positioned on the surface rectangular to a path center of a tube 10 to be worked. The gap G1 between roller flanges is set to zero as possible and the gap G2 is set to a prescribed gap. When a plug 15 is inserted into the calibers and the tube 10 to be worked is set to be pulled in the extending direction, the tube 10 to be worked is pressed and reduced in thickness by the plug 15 and the caliber rolls 11 and part of the reduced thickness is expanded into the roll gaps G2 to generate fin parts. Since the reduced thickness parts of the tube stock of deviated thickness passes the roll gap parts G1, a projection is not generated. A finned tube having no excess projection on the outer surface can be manufactured and this is effective to the protection against the tool.