PURPOSE: To make the operation of a mandrel and a shell easy by interlocking the revolving shaft of arm supporting the roll of a mandrel rolling mill and the back and forth movement of the restraining bar which moves the mandrel bar and operating a roll mechanism reversibly.

CONSTITUTION: Plural units of roll mechanisms 6 which support a mandrel 1 and a shell 2 are disposed on the inlet table of a rolling mill. The mechanisms 6 are formed of arms 62, 62a fixed to respective revolving shafts 61 and rolls 64, 64a fixed to the shafts 63, 63a between the arms 62, 62a. The arms 62, 62a are turned reversibly in synchronization with a restraining bar 31 by the driving of the restraining bar 31 provided to the restraining mechanism 3 of the mandrel bar 1 with a gear mechanism 81 and shaft 83 interposed between a pinion 34 and a driving motor 8. The collision between the mandrel bar 1 and the roll 6 is prevented, thereby improving the working efficiency of rolling.