There is provided a method for heating a thermoplastic plate to be subjected to bending which is horizontally arranged while holding at least part of a peripheral edge portion of the thermoplastic plate, causing a portion inside the peripheral edge portion to sag under a self-weight, and bending the thermoplastic plate to a desired curvature. The method includes applying tension in a planar direction of the thermoplastic plate at the time of holding at least the part of the peripheral edge portion of the thermoplastic plate in a molding frame defining a peripheral edge shape in a shape as a goal for reshaping. Since the thermoplastic plate is pulled in the planar direction during the heating of the thermoplastic plate, moderate tension acts on the thermoplastic plate to prevent breakage. The degree of curvature of the thermoplastic plate can be adjusted by adjusting the mass of each weight.