Manufacturing method for hollow rack shaft, and hollow rack shaft

A manufacturing method for a hollow rack shaft comprising:

• using a tubular member as a raw material, having a planar flat portion formed in part of a tubular body portion;
• and
• forming rack teeth at the flat portion;
• wherein
• the tubular member is held with a back die having a tooth-shaped portion substantially symmetrical with the rack teeth so that a surface of the flat portion is in contact with the tooth-shaped portion,
• the back die having protrusions is arranged so that the protrusions face groove portions of the tooth-shaped portion across the flat portion,
• the rack teeth are formed by pressing the back die against the flat portion such that a surface of the back die opposite the plurality of protrusions and an inner peripheral surface of the tubular body portion define a hollow gap therebetween, and
• the surface of the back die opposite the plurality of protrusions is parallel to the planar flat portion.