To provide a worm gear device capable of making compatible the simplification of production processes and the securement of sufficient load bearing capacity by improving the structure of a worm wheel with resin teeth and a method of manufacturing the worm wheel used for the worm gear device.

This worm gear device 5 comprises a cylindrical worm 51 and the disk worm wheel 52. A part of the resin teeth arranged parallel to each other on the outer periphery of the worm wheel 52 are formed in round bottom teeth 7 each having an arcuate tooth bottom curved while recessing the center in the direction of the tooth width. The remaining teeth are formed in flat bottom teeth each having a flat tooth bottom in the direction of the tooth width.