Provided is a thermal activation device including a thermal activation head (11) for thermally activating a heat-sensitive adhesive layer of a sheet material (3) having a printing layer provided on one surface of a sheet-like base material and having the heat-sensitive adhesive layer provided on the other surface thereof, and a platen roller (12) for holding and conveying the sheet material (3), the platen roller (12) being brought into press contact with the thermal activation head (11). Moreover, the thermal activation head (11) thermally activates the heat-sensitive adhesive layer asymmetrically with respect to a centerline in a width direction perpendicular to a conveying direction of the sheet material (3). Furthermore, a plate spring (18) which urges the sheet material (3) to be pressed onto a peripheral surface of the platen roller (12) is provided, the plate spring (18) being located on an upstream side of the thermal activation head (11) in the conveying direction of the sheet material (3).