In gearbox design, small size, light weight, and long service life are important factors that must be considered. The planetary gear train structure has been widely used to realize these characteristics. In this study, the effects of increasing the torque on and changing the rotation direction of a planetary gearbox on the dynamic load sharing among the planet gears were analyzed experimentally using a planet carrier manufactured at an industrial site. When the number of planet gears was even, one pair of planet gears exhibited higher load sharing than the other two pairs among the three pairs of planet gears, where the two gears in each pair faced each other directly, regardless of the rotation direction of the gearbox. In addition, increasing the torque of the planetary gearbox improved the mesh load factor. The mesh load factor varied significantly as to the rotation direction changed, due to the phase change of the carrier pinhole position error.