A theoretical method of obtaining the nominal stress in the rim of a planet gear with both a thin rim and the clearance between the rim and the gear shaft is shown by using an equivalent ring. In the analysis, the boundary position between the region where the rim is in contact with the shaft and that where they are out of contact with each other is assumed because the boundary position depends on the tooth load and the clearance in the case of the constant rim thickness. Then after the bending moment in the one region is compared with that in the other one at the assumed boundary position, the true boundary position where the bending moment in the one region is equal to the other one is determined. Using the true boundary position obtained, the bending moment and the circumferential force in the rim are obtained in order to obtain the nominal bending and circumferential stresses in the rim of the planet gear. Further, effects of tooth load and the clearance on the stress in the planet gear are investigated by the method obtained.