Intended is to provide a mandrel mill capable of manufacturing a seamless pipe having no flaw such as a necking flaw. The mandrel mill has a plurality of hole type roll stands installed consecutively, and a mandrel bar (3) is arranged in the forging roll die formed of those hole type roll stands, thereby to draw and roll a hollow shell (2) continuously. A roll die (4) for at least a first stand and a second stand is arranged to satisfy the conditions expressed by the following Formulas (1) to (4): b = 10a + 1.5... (1); b >= 10a - 0.2... (2); b = -a + 1.15... (4), wherein a = S/R1, and b = C/(R1 - S).