PURPOSE: To uniformize rolling distribution and to decrease ununiform thickness by piercing and rolling a seamless steel tube with piercing rolls where the majority of the roll is parallel with a pass center when a seamless steel tube is set to a piercer in a manufacture of the seamless steel tube using a Mannessman piercer.

CONSTITUTION: A draft becomes maximum in a gorge part but its distribution becomes uniform in the case of a barrel type roll since the majority of the roll is pierced and rolled with a piercing roll 1 parallel with the pass center when it is set to the piercer. Consequently, unnecessary swell of the element tube to the direction of a guide shoe is relieved, a gap between a plug and a shell in the direction of the guide shoe becomes small, the plug is stabilized in the shell, ununiform thickness is restrained, local damages to the plug and the guide shoe can be restrained and the lives of the plug and the guide shoe can be prolonged.