To achieve an improvement in the uniformity of pipe wall thickness in a piercer mill to be utilized in the first process for manufacturing a seamless steel pipe.

A piercer mill guide comprises a guide shoe provided with an opening for making a drive roller shoe and a billet abut to each other and a concave portion which slides along the outer diameter of the billet and a position adjusting unit provided on both drive roller shoe ends of the guide shoe and latched to a mill housing, with the guide shoe being free to tilt.