Provided is a thermal activation device capable of preventing a heat-sensitive adhesive sheet from being partially excessively heated, keeping a short distance between a contact between a thermal head and a platen roller, and a discharge port, and preventing a structure of the thermal activation device from being complicated and a size thereof from increasing. While a heat-sensitive adhesive sheet (2) is transported along a transport path (15) through rotations of insertion rollers (3) and a platen roller (5), a heat-generating portion (4a) of the thermal head (4) is caused to generate heat, thereby thermally activating a heat-sensitive adhesive layer of the heat-sensitive adhesive sheet (2). When a trailing edge of the heat-sensitive adhesive sheet (2) reaches a position where the trailing edge thereof is not in contact with the platen roller (5), a transporting force is not transmitted to the heat-sensitive adhesive sheet (2), thereby stopping transportation thereof. At that time, an adhesion prevention member (6) is allowed to enter the transport path (15) to lift and hold the trailing edge of the heat-sensitive adhesive sheet (2) to a position where the trailing edge thereof is not in contact with the thermal head (4).