A grinding apparatus including a robot, a grinding tool attached to the robot, a force sensor configured to detect a force exerted on the grinding tool, and a controller connected with the force sensor and configured to control the robot. The controller includes a variation acquiring section configured to acquire the present position of the robot by pressing the grinding tool against a reference surface in such a manner that a pressing force detected by the force sensor is constant, and to acquire a difference between the acquired present position and a reference position of the robot stored in advance, the difference being acquired as a variation of the grinding tool.