PURPOSE: To improve the productivity and to reduce the product cost without making a defect such as a crack on a product tube by determining a proper range of a quantity of state regarding the rolled state of a metallic tube and changing the advancing speed or rotating speed when the rolling advances beyond its range.

CONSTITUTION: The quantity of state regarding the rolled state is detected and when this detected result exceeds a preset upper limit value by a build-up made on a tube A being a rolling object, the advancing speed per rotation of the tube A is reduced by the increase of the advancing speed of the tube A or the speed of rotation of rolling rolls 1, 2, 3 before a defect such as a crack caused by the build-up in generated on the product tube. Further, when the disappearance of such build-up is recognized by the fact that a detected result exceeds the lower limit value set within a specified proper scope or converges to a fixed value within the scope, the amount of advance per rotation of the tube is returned to a high level by the increase of the advancing speed of the tube A or the decrease of the speeds of rotation of the rolling rolls 1, 2, 3, consequently, a crack, etc., are not generated and rolling can be performed at a speed as high as possible.