A vacuum thermoforming apparatus including: a molding machine on which a window base material is mounted; and a pressure supply machine coupled to the molding machine and configured to supply a pneumatic pressure toward the molding machine. The molding machine includes a mounting part having a curved surface-shaped mounting surface, and a coupling part having a structure for coupling with the pressure supply machine and a curved portion along the shape of the mounting part. The pressure supply machine includes: a cover part facing the mounting surface; and a side wall extending from the cover part to define an inner space in the pressure supply machine, the side wall having a curved upper surface so as to engage with the coupling part.