PURPOSE: To beforehand prevent the generation of abnormality of peeling, buckling, etc., by restraining bottom flare in the terminal part of tube at the time of skew rolling using a piercer, elongater, etc.

CONSTITUTION: The terminal of tubing 4 is detected with a terminal detector 7 which is arranged in front of inclined rolls 1, 1. Based on the detected result with the terminal detector 7, operation command is sent to a machine 5 for adjusting opening degree of roll and machine 6 for adjusting guide position from a control part 9 and the opening degree of roll between the inclined rolls 1, 1 and the position of disk rolls 2, 2 are respectively changed by prescribed amounts by operating them. That is, the range of a prescribed length from the terminal part of the tubing 4 is rolled under the opening degree of roll larger than another part and in a state that intervals, which are increased accompanying to that, between the peripheral surfaces of the inclined rolls 1, 1 and the side faces of the disk rolls 2, 2 are kept in a prescribed dimension. In this way, bottom flare is restrained.