PURPOSE: To reduce the time and cost for slitting with a relatively simple installation by fixing one of a lower or upper die to a pipe then pressing the other to the pipe thereby slitting the pipe.

CONSTITUTION: A pipe P is placed on the supporting bases 4, 4W of a carriage 1 and after one end thereof is held by a chuck 11, a lower die 14 is inserted therein and is positioned by a positioning arm 20. A hydraulic cylinder 19 is actuated to lower an upper die 17 and to fix the pipe P and thereafter a hydraulic cylinder 15 is actuated to rise the die 14 thereby slitting the pipe P by blanking. After the cylinders 15 and 19 are actuated reversely, the pipe P is rotated by a prescribed angle by a turning mechanism 6 and similarly the slitting by blanking is accomplished by a press mechanism 13. The pipe P is turned one round then the carriage 1 is advanced at a prescribed interval by an indexing mechanism 21 and the circumferential slitting is performed in the same way as mentioned above. The same operation is successively repeated.