To provide a method and an apparatus for forming an internal gear by means of which no under fill occurs and consequently a cycle time of internal gear formation can be shortened even when the internal gear is formed by plastic working of a thin blank.

The method for forming the internal gear W is provided by which the cylindrical internal gear is formed by fitting the blank P to a mandrel 2 having a tooth profile 2c on the circumferential surface and pushing the blank P to the mandrel 2 by pushing a drawing roller 1 to the blank P, wherein the drawing roller 1 is used which has, at two positions, circular arc-portions R1 and R2 to be abutted on the blank P, the outer diameter D2 of the circular arc-portion R2 to be abutted on the blank P later being larger than the outer diameter D1 of the circular arc-portion R1 to be abutted on the blank P first, and the drawing roller 1 is moved in a direction parallel to the axial center M of the mandrel 2, and thus, the cylindrical internal gear W is formed.