An electrothermal heating device for heating a print medium includes an endless belt, a first electrode and a second electrode. The endless belt rotates in a rotational direction about a rotation axis that defines an axial direction, so as to generate heat when the endless belt rotates and is supplied with power. The endless belt includes a base portion made of a nanocomposite material having a carbon filler. The first and second electrodes are in contact with the base portion of the endless belt. The first and second electrodes extend in the axial direction of the endless belt, and are spaced apart in the rotational direction of the endless belt. A volume resistivity of the base portion of the endless belt in the rotational direction is less than a volume resistivity of the base portion in the axial direction.