Recently information recording media (reversible or irreversible information recording media (re-writable card, re-writable sheet) provided with a recording portion comprising a reversible heat-sensitive recording layer) has been widely used, in which coloration, color change and erasing of color can be carried out reversibly or irreversibly repeatedly by heating on a base material in a shape of film, sheet or card made of a paper, non-woven fabric, woven fabric, synthetic resin such as vinyl chloride or polyethylene terephthalate, metal, glass, hard converted paper (paper for a card being harder than a cardboard and produced by curing a vegetable fiber or the like under pressure), or the like.
For example, a heating head having a structure as shown in FIG. 12 is known as a heating head for heating such a medium (for example, see JP 2004-268256 A). In FIG. 12, a heating head is configured such that a glass layer (glaze layer) not shown is provided on one surface of a head substrate 51 made of alumina or the like, a heating element 52 is provided thereon, and electrodes 53 are provided at both ends of the heating element. The electrodes 53 are designed such that wiring is led out from the head substrate 51 and is connected to a circuit board (not shown) located in the neighborhood of the head substrate 51 to enable a voltage to be applied to the heating element. As a result, a voltage is applied to the both ends of the heating element 52 through the pair of electrodes 53 and an electric current is flowed to generate heat on the heating element 52, thus enabling a temperature of the heating element 52 to be controlled by an amount of current. This head substrate 51 is held by adhering to a base 54 made of a metal plate or the like with an adhesive 55. In the example shown in FIG. 12, a concaved portion 56 is formed partly on the base 54 under the heating element 52, and a material having applicable heat conductivity different from that of the base is filled in the concaved portion 56 so as to inhibit escaping of heat from the head substrate 51 to the base 54.