A heater device has a heater body and a heater case. The heater body has a heat generating part generating heat and radiates the heat supplied from the heat generating part. The heater case is attached to an interior member provided in an interior and houses the heater body, such that an interior-side surface of the heater body is located on a back side of the interior member. The heater case is provided with a ventilation passage through which a space outside the heater case located on the back side of the interior member communicates with the interior-side surface of the heater body.