To reduce cost by embossing and molding embossments and/or recesses to a circumferential wall in a grooved shape over entire length and conducting reinforcement in the at least axial direction without using a reinforcing material.

The external embossments 4 of a rhombus or the like are embossed and molded to the whole circumferential external wall 3 of the drill bit tube 1 while the embossments 4 are surrounded by corresponding rhombic recesses 5. Consequently, rhombic recesses 4' surrounded by corresponding rhombic embossments 5' are formed to a circumferential interior wall 2, and the thickness of a material is equalized as a whole. The recesses 5 form spiral paths on the outer circumferential surface of the tube 1 in parallel with the side walls of the embossments 4. Since the tube 1 is reinforced by the embossments 4 and the recesses 5 and a frictional region brought into contact with a drilled wall is reduced, friction is lowered. Cutting chips generated in the case of the rotary operation of the tube 1 is discharged easily by the spiral path. Accordingly, a wall surface can be reinforced at a low cost, and driving force can be lowered.