Providing a thermal head capable of preventing the adherence of a thermally active component, a thermal activation device for thermally active sheet employing the thermal head, and a printer assembly employing the thermal activation device. A thermal head has an arrangement wherein a heat storage layer (glaze layer 2) is formed on a heat releasing substrate (ceramic substrate 1), wherein plural heat generating resistances (3) and electrodes (4a, 4b) for power supply to the individual heat generating resistances are formed on the heat storage layer thereby forming an array of heat generating elements, and wherein a protective layer (7) covers the top surfaces of these parts; and applies thermal activation energy to a print medium (heat-sensitive self-adhesive label R) including a thermally active component by supplying power to the heat-generating element array, the thermal head provided with two substantially parallel lines of anti-adherence layers against thermally-active-component (8a, 8b) on the protective layer in a manner to sandwich a protective layer portion directly above the heat-generating element array.