Resin gear

A resin gear having a plurality of teeth having no torsion angle, wherein:

• in a tooth, a tooth face that is a predetermined area from a tooth crest towards a tooth root side serves as a tooth profile modification area, and a tooth surface excluding the tooth profile modification area serves as an involute profile area,
• in which the tooth profile modification area has a tooth surface that is formed by smoothly connecting, in a tooth width direction, surfaces formed by a tooth profile cross-section obtained by equally dividing, in the tooth width direction, the tooth surface from a tooth width direction center to a tooth width direction end, so that the tooth profile modification area includes
• (1) a linear standard profile portion formed by an involute curved line from the tooth crest of the tooth towards the tooth root side and
• (2) a profile modification portion in which a tooth thickness continuously decreases from the standard profile portion along a tooth width direction and the tooth thickness continuously decreases from a tooth root end side towards the tooth crest;
• a contacting section becomes elastically deformed as a result of the resin gear coming into contact with a meshing mating gear, and (1) a tooth width direction length of the contact surface gradually increases from a minute width to a full tooth width from the tooth crest side towards the tooth root side, or (2) the tooth width direction length of the contact surface gradually decreases from the full tooth width to the minute width from the tooth root side towards the tooth crest side.