Abstract: A heater member (1a) includes a support (10), a heating element (20), and at least one pair of power supply electrodes (30). The support (10) is made of an organic polymer and has a sheet shape. The heating element (20) is made of a polycrystalline material containing indium oxide as a main component and in contact with one principal surface of the support (10). The power supply electrodes (30) are in contact with one principal surface of the heating element (20). The heating element (20) has a sheet resistance in the range from 10 to 150 ?/sq. The heating element (20) has a thickness of more than 20 nm and not more than 200 nm. The internal stress of the heating element (20) as measured by an X-ray stress measurement method is 500 MPa or less.