An optical disk drive includes a motor base, a rotating shaft, a rotor and a disk mounting structure. The rotating shaft is rotatably disposed on the motor base. The rotor is disposed on the rotating shaft with part of the rotating shaft protruding from the rotor. The disk mounting structure includes a mounting portion, a fitting portion and a ball. The mounting portion is disposed on the rotating shaft for carrying an optical disk. The fitting portion is disposed on the mounting portion to be buckled into the hole of the optical disk. The lateral surface of the fitting portion has a cavity. The ball is movably disposed inside the cavity and may be pulled or attracted by a predetermined pulling force. When the disk mounting structure rotates, the ball will press the optical disk because the centrifugal force of the ball is larger than the predetermined pulling force.