PURPOSE: To provide a titled piercer capable of efficiently mending and exchanging disks without moving work rolls vertically by horizontally turning the guide disks used for supporting a material between upper and lower rolls around the fulcra of a housing, in a piercer of a seamless steel pipe.

CONSTITUTION: Horizontal guide disks 8 for supporting a material 1 between work rolls 7 of which axes are crossing each other are horizontally turned around the fulcrum pins 10 of housing posts 3 to mend and exchange the disks 8 on supporting beds 20. In this way, the disks 8 are exchanged in a free space without moving the work rolls 7 vertically to improve the operating efficiency.