Thermoforming apparatus and thermoforming method

A thermoforming apparatus, which is for mold-shaping a sheet with respect to a base material or bonding said sheet to said base material, is provided with: a lower frame, which has a surrounding frame wall and a frame bottom in which a vacuum vent hole is formed and which forms a space for accommodating the base material; a heating plate, which has a heating surface and is configured so that the heating surface comes into close contact with the upper edge of the surrounding frame wall; a base with a base material-holding section capable of holding the base material; a sealing frame, which is provided so as to protrude from the base-setting surface of the frame bottom and, in planar view, surrounds the entire circumference of the base material-holding section; and a sheet-gripping section for gripping the peripheral edge of the sheet without gaps over the entire perimeter thereof, the section being provided inside the lower frame so as to be vertically movable between an elevated position in which the sheet is