A pressure-sensitive adhesive strength exhibiting unit including: a thermal head including heat-generating elements aligned in a row, for heating the pressure-sensitive adhesive label from the pressure-sensitive adhesive layer side to cause each of the heat-generating elements to form a bore in the functional layer; a platen roller for conveying the pressure-sensitive adhesive label while sandwiching the pressure-sensitive adhesive label between the thermal head and the platen roller; and a control part for applying heat energy to each of the heat-generating elements independently, wherein when the control part continuously forms perforation lines in which a plurality of the bores are aligned in a row by repeating the application of heat energy, the control part applies high heat energy, whose energy amount is higher than an energy amount of heat energy applied to the heat-generating elements during formation of a previous perforation line, to the heat-generating elements to form the perforation line.