A heater includes an electrode, a heat generator, and a plurality of layers including a first layer and at least one additional layer disposed in an opposite side with respect to a surface on which the electrode is disposed. The at least one additional layer includes at least one of a plurality of portions, a gap at a location corresponding to the electrode, existing between the plurality of portions and a single portion, at least a part of the single portion corresponding to the electrode, being relatively thinner than a part of the single portion corresponding to the heat generator.