To provide a worm gear device capable of restricting a surface of a pitch circle of a worm wheel and quantity of rattle of a worm in the vertical direction to automatically eliminate backlash between them.

This worm gear device 1 has the worm wheel 3 rotatably supported by a support base 2 through a first bearing, a worm supportable holder 5 having a second bearing for rotatably supporting the worm 4 to be engaged with the worm wheel 3 and fitted to the support base 2 through a third bearing to swing, and a coil spring 58 for pushing the worm 4 to the worm wheel 3. Each of the bearings are arranged to eliminate looseness in the thrust direction, and the second bearing is arranged so that the center axis of rotation thereof passes through a pitch point 63 of the worm wheel 3 and the worm 4 and becomes in parallel with a tangent 64 of the pitch circle 14 of the worm wheel 3, and the third bearing is arranged so that the center axis 36 of rotation thereof is separated from a surface, wherein the pitch circle 14 passes, in a direction of a parallel line 65 in parallel with the center axis 16 of rotation of the worm wheel 3 and becomes in parallel with the tangent 64.