PROBLEM TO BE SOLVED: To provide a working method by which a tube having the grooved inside surface the lead angle of the internal grooves of which is larger is easily obtained. SOLUTION: A floating plug 2 and a grooving plug 4 which is connected to the floating plug 2 with a connecting rod 3 are arranged in a metallic tube 1, the floating plug 2 is stopped in a drawing die 9 part by passing the metallic tube 1 through the drawing die 9 and, in the case the metallic tube 1 is finished into of the prescribed outside diameter succeedingly passing through a finishing die 7 after forming a plurality of grooves 8 on the inside surface of the metallic tube 1 by pressing the metallic tube 1 which is passed through there in a position in which the grooving plug 4 is present onto the grooving plug 4, the grooving work of the inside surface is performed while rotating the metallic tube 1 in the same direction (the arrow B) as the rotational direction (the arrow A) of the grooving plug 4. In such a case, by rotating the drawing die 9 in the same direction as the rotation of the metallic tube 1, the drawing force in the drawing die 9 part can be decreased.