PURPOSE: To shorten the time of rolling cycle, by quickly removing rolled round pipe together with the mandrel from the pass line in the direction of backward and downward, and at the same time, by inserting the mandrel for carrying out the sizing work.

CONSTITUTION: The round pipe is sent forward in the arrowed direction 2 on the pass line A-A through the charging unit 1, is rolled into a differently sectioned round pipe by the mill 3, and this pipe under the condition being inserted with the mandrel is supported by the mandrel holder 4. The round pipe finished the rolling work as holding the mandrel inside is discharged to the beneath of the mandrel holder 4, and is sent forward along the pass line A-A to the backside of the mill in the arrowed direction 6 passing under the mandrel sizer 5. The front tip of the round pipe is caught by the stripper block 7, and the front tip of the mandrel is caught by the stripper roll 8 and is pulled away in the arrowed direction 9. After that, the round pipe is sent to the next process in the arrowed direction 10; and the mandrel is recycled along the arow marks 11, 12, 13, being properly cooled and applied with lubricant on the midway, and is returned onto the pass line A-A by the mandrel feeder 14.