To automatically adjust the direction of the oval part of the shaft end on the driving side of a rolling roll.

When the oval part 20 is in a prescribed direction, measuring devices 21, 22 are arranged at the equal distance outside radii passing through the axis line O and passing through the vicinities of the boundaries between the cylindrical surface 20c of one side and flat surfaces 20a, 20b on both sides. In the state of (1), detected distances L11, L12 are equal. When the oval part 20 is inclined like (2) or (3), difference is produced between the detected distances L21, L22 or L31, L32 and it is easily detected that the direction of the oval part 20 is inclined. By rotationally driving the rolling roll and making the state like (1), the direction of the oval part 20 is automatically adjusted.