Disclosed is a gas furnace for indoor heating. The gas furnace includes a burner to generate high-temperature exhaust gas, an exhaust flow path, a blower to suction indoor air through a recovery flow path, a supply flow path to guide the indoor air to the indoor space after undergoing heat exchange in the exhaust flow path, and a fuel supply unit including a fuel supply line and a fuel discharge line, configured to supply fuel to the burner, and a valve between the fuel supply line and the fuel discharge line. The valve includes a step motor, and a blocking member coupled to a rotating shaft of the step motor and configured to move straight via by driving of the step motor, and an opening degree of the valve between the fuel supply line and the fuel discharge line is adjusted by the straight movement of the blocking member.