Disclosed is a variable spoiler apparatus of the rear bumper for vehicles. The variable spoiler apparatus includes a linkage device, installed on a bumper back beam, and varies in length in an up-down direction during a rotation. A spoiler is coupled to the linkage device and is able to move in the up-down direction by the rotation of the linkage device. A first drive device is installed on the bumper back beam. The first drive device is provided with a first rotating shaft coupled to the linkage device to transmit rotating force. A guide is rotatably installed on the bumper back beam and is able to extend in the up-down direction. A second drive device is coupled to the guide so as to be movable in the up-down direction. When the second drive device is operated, the spoiler is tilted by a length variation operation of the length-variable unit.