Vacuum forming apparatus and vacuum forming method

A vacuum forming apparatus comprising:

• a forming die having at least one suction hole for creating a vacuum;
• a plurality of holding devices configured to hold at least two opposite sides of a resin sheet that has been softened by heating in order to be molded by the forming die;
• a pressing device configured to be moved relative to the forming die to close a space between the forming die and the pressing device such that an airtight state is created between the resin sheet and the forming die;
• and
• a pair of supplemental holding devices disposed in two positions on one of the sides of the resin sheet extending between the two opposite sides held by the holding devices, with each of the supplemental holding devices including a clamp member configured to clamp the resin sheet and a support member configured to extend from the clamp member for supporting a bottom surface of the resin sheet, the supplemental holding devices being movably arranged to move toward each other along the one of the sides of the resin sheet extending between the two opposite sides held by the holding devices to form a localized sag area between the two positions where the resin sheet will be made to locally sag in a part of the one of sides of the resin sheet extending between the two opposite sides held by the holding devices,
• the clamp members being configured to clamp the resin sheet in the two positions, and the support members being configured to extend from the two positions toward inside of the resin sheet along two side portions of the localized sag area to support loads acting on the two side portions of the localized sag area.