A cover sheet supply apparatus having variable clamps for a thermoforming machine, the thermoforming machine including a heating unit for heating the cover sheet provided to be adhered to an interior material of a vehicle, the cover sheet supply apparatus comprising: a support frame provided in the cover sheet supply apparatus; a pair of longitudinal guides disposed in the support frame at positions spaced apart from each other by a predetermined distance, each of the longitudinal guides comprising a longitudinal rail, with a longitudinal fixed unit fixed to the longitudinal rail; a pair of lateral guides disposed in the support frame on opposite sides of the longitudinal guides at positions spaced apart from each other by a predetermined distance, each of the lateral guides comprising a lateral rail, with a lateral fixed unit fixed to the lateral rail; a plurality of longitudinal movable clamps installed on each of the longitudinal rails at regular intervals to clamp the cover sheet, the longitudinal movable clamps being successively connected to each other by a longitudinal link from the longitudinal fixed unit to the lateral guides; a plurality of lateral movable clamps installed on each of the lateral rails at regular intervals to clamp the cover sheet, the lateral movable clamps being successively connected to each other by a lateral link from the lateral fixed unit to the longitudinal guides; a lateral moving means provided on the fixed frame, the lateral moving means configured to move the longitudinal guides forwards and backwards in the lateral direction; and a longitudinal moving means provided on the fixed frame, the longitudinal moving means configured to move the lateral guides forwards and backwards in the longitudinal direction, wherein when the cover sheet is heated by the heating unit and thus expanded and sagged, the lateral moving means and the longitudinal moving means are adapted to move the longitudinal guides and the lateral guides so that the cover sheet is stretched, characterized in that each of the longitudinal link and the lateral link comprises a plurality of link sticks coupled to each other by a hinge. a support frame provided in the cover sheet supply apparatus; a pair of longitudinal guides disposed in the support frame at positions spaced apart from each other by a predetermined distance, each of the longitudinal guides comprising a longitudinal rail, with a longitudinal fixed unit fixed to the longitudinal rail; a pair of lateral guides disposed in the support frame on opposite sides of the longitudinal guides at positions spaced apart from each other by a predetermined distance, each of the lateral guides comprising a lateral rail, with a lateral fixed unit fixed to the lateral rail; a plurality of longitudinal movable clamps installed on each of the longitudinal rails at regular intervals to clamp the cover sheet, the longitudinal movable clamps being successively connected to each other by a longitudinal link from the longitudinal fixed unit to the lateral guides; a plurality of lateral movable clamps installed on each of the lateral rails at regular intervals to clamp the cover sheet, the lateral movable clamps being successively connected to each other by a lateral link from the lateral fixed unit to the longitudinal guides; a lateral moving means provided on the fixed frame, the lateral moving means configured to move the longitudinal guides forwards and backwards in the lateral direction; and a longitudinal moving means provided on the fixed frame, the longitudinal moving means configured to move the lateral guides forwards and backwards in the longitudinal direction, wherein when the cover sheet is heated by the heating unit and thus expanded and sagged, the lateral moving means and the longitudinal moving means are adapted to move the longitudinal guides and the lateral guides so that the cover sheet is stretched, characterized in that each of the longitudinal link and the lateral link comprises a plurality of link sticks coupled to each other by a hinge.