Abstract: Disclosed herein is a cover sheet supply apparatus having variable clamps for a thermoforming machine. The apparatus includes a support frame (100); longitudinal guides (200) which are disposed in the support frame and each of which includes a longitudinal rail (210) and a longitudinal fixed unit (220); lateral guides (300) which are disposed in the support frame on opposite sides of the longitudinal guides, and each of which includes a lateral rail (310) and a lateral fixed unit (320); longitudinal movable clamps (230) which are installed on each longitudinal rail and are connected to each other by a longitudinal link (400); lateral movable clamps (330) which are installed on each lateral rail and are connected to each other by a lateral link (500); a lateral moving means (600) which moves the longitudinal guides in the lateral direction; and a longitudinal moving means (700) which moves the lateral guides in the longitudinal direction.