Provided is a method of manufacturing a resin molded gear, which is to be integrally formed by injection molding, and includes: a tooth portion formed along an outer peripheral surface of a rim; a web extending along an inner peripheral surface of the rim; and a gate portion arranged at a boss, which joins to at least part of the web and is formed on a core portion located at a center axis, the method using a synthetic resin having a melting temperature of Tm° C., the method including: injecting and loading the synthetic resin molten at the melting temperature of Tm° C. into a cavity of a mold for forming the resin molded gear; and setting, when the gate portion is solidified, a thickness center temperature T1 of the web to (Tm−20)° C. or more to (Tm+20)° C. or less and a surface temperature T2 of the tooth portion to (T1−50)° C. or less.