The invention relates to an apparatus for making a seamless hollow body (10) from a solid round block (7) of steel with a diameter <95% of the diameter of the solid round block by means of a two-roll cross-rolling mill with a piercing mandrel (3) held between the inclined roll (1) and including a piercer (5) and at least one smoothing part (4) using pass-closing guides, or by means of a three-roll cross rolling mill with a piercing mandrel held between the inclined rolls and including a piercer and at least one smoothing part, wherein the distance of the rolls is adjusted in a particular manner at the narrowest cross-section (2) in relation to the diameter of the used round block, and the position of the piercing mandrel is adjusted in relation to the narrowest cross-section of the rollers.