To prevent condensation and solidification of polishing particles in a gear part of an internal gear to restrict the occurrence of a failure due to the condensed and solidified grinding particles.

This grinding device is formed of a carrier 50, which holds a work to be ground and which is engaged with a sun gear and an internal gear and which revolves and rotates in response to rotation to the sun gear and the internal gear, and an upper polishing plate 20 and a lower polishing plate 10 for pinching the work to be ground from over and under the material held by the carrier 50, and a grinding liquid supply unit for supplying the grinding liquid between the upper polishing plate 20 and the lower polishing plate 10. In this grinding device, the grinding liquid, which reaches the internal gear 40, passes through the top surface of a gear part 40a, and reaches the top surface of a ring part 40b to grind the work W, while restricting a leak of the grinding liquid on the ring part 40b outside.