To secure adequate printing density and suppress damage to a medium to be printed, even when printing is increased in speed.

A thermal printhead includes: an insulation substrate comprised of a ceramic substrate 22 and a glaze layer 25; a resistor layer 26 and an electrode layer 28 laminated on a surface of the glaze layer 25; and a protective film layer 29 covering the substrate and the layers. In the resistor layer 26, heating resistors are formed that are arrayed at intervals in a main scanning direction on a surface of the glaze layer 25 and extending in a sub-scanning direction, respectively. In the electrode layer 28, electrodes are formed that are connected to the heating resistors at both ends in the sub-scanning direction. The heating resistors are divided into a first heating part 61, a second heating part 62, and a third heating part 63, toward a downstream side in the sub-scanning direction. The first heating part 61 is thinner than the second heating part 62.