To reduce noise generated by a pair of gears when they mesh with each other and to decrease an error in rotation transmission, and further to prevent a reduction in strength of a gear tooth.

The gear G1 includes a plurality of teeth 1 and transmits the rotation by engagement of the teeth. At the tooth top portion of each tooth 1, the diameter of a tip circle is varied from one end 5 toward the other end 6 in the breadthwise direction of the tooth, and a tooth crest 7 is formed to have a portion inclined from one end 5 toward the other end 6. At the dedendum portion of each tooth top 1, the diameter of a dedendum circle is varied from one end 8 toward the other end 9 in the breadthwise direction of the tooth, and the dedendum of the tooth is so shaped as to be inclined from one end 8 toward the other end 9. Accordingly, it is possible to reduce the noise generated by a pair of gears when they mesh with each other and to decrease the rotation transmission error, and further to prevent the strength reduction of the gear tooth.