To solve the problem that a tooth striking noise is generated from an intermeshed part of a worm and a worm wheel owing to a backlash by undergoing a reverse input from a road surface, then the backlash is needed to strictly controlled; it increases in cost; a rubber made damper is permanently set in fatigue owing to a long period usage to increase a noise.

First and second ends 19a and 19b of a worm 19 are formed of synthetic resin members 29 and 30. An intermediate part 19c provided with a tooth 60 of the worm 19 is formed of a metal member 31. The synthetic resin members 29 and 30 are integrally and rotatably combined with the metal member 31. Polyamide resin having elasticity is used as synthetic resin members 29 and 30.