A heater includes a fixing device including a heater substrate, electrodes, a heating element, and a heat conducting member. The heating element is disposed on a facing surface of the heater substrate that is to face a sheet, and includes a plurality of heating element pieces arranged in a line in a main scanning direction of the sheet with a gap therebetween. The heat conducting member stores heat generated from the heating element and radiates the heat toward the sheet passing over the gap.