A heating device includes a rotatable film, a heater disposed inside the film and including a substrate that extends along a first direction and having two surfaces opposite to each other, and a heater element on one of the surfaces of the substrate, and a heat conductor including a first portion contacting the other surface of the substrate, and a second portion that is adjacent to the first portion in a second direction perpendicular to the first direction and does not contact the other surface of the substrate. A width of the second portion is wider than the heater element in the second direction.