PURPOSE: To prevent the deterioration of the strength of the rack tooth, by making the tooth height of a pinion gearing with a rack at the rotary position of the rack where the gear ratio is at the lowest to be shorter than the tooth height of other teeth and working the rack tooth profile by said pinion tooth profile.

CONSTITUTION: In the proximity of the neutral position of a pinion 4 where the gear ratio is at the lowest, the teeth 14, 15 of the pinion 4 gearing with the rack is constructed such that the distance between the addendum arc 17 and a referential pitched circle 18 is shortest shorter than the distance of other teeth 12, 13, 16 while the tooth height of the teeth 13, 16 is made higher than that of the teeth 14, 15 but shorter than that of the tooth 12 thus to form the pinion tooth profile. The tooth profile of the rack 7 is formed by working the rack 7 by means of said pinion tooth profile while performing the relative motion to achieve the predetermined variable gear ratio between the rack and the pinion.