A method for reducing the dew point of a furnace atmosphere gas in a continuous annealing furnace for annealing a metal strip in a reducing atmosphere by passing the metal strip through a heating zone and a cooling zone in this order or through a heating zone, a soaking zone, and a cooling zone in this order, comprising: a step (a) for providing a circulator that includes a heat exchanger for heat exchange between a low-temperature gas and a high-temperature gas, a gas cooler for cooling a gas, and a dryer for dehumidifying a gas to a dew point of - 45°C or less; a step (b) for sucking part of the atmosphere gas from the heating zone and/or the soaking zone; then a step (c) for passing the sucked part of the atmosphere gas through a high-temperature gas passage of the heat exchanger and decreasing the temperature of the sucked part of the atmosphere gas by heat exchange with a gas in a low-temperature gas passage; then a step (d) for mixing the part of the atmosphere gas having a decreased temperature with part of an atmosphere gas sucked from the cooling zone to further decrease the temperature of the part of the atmosphere gas; then a step (e) for passing the part of the atmosphere gas further cooled by mixing with the part of the atmosphere gas sucked from the cooling zone through the gas cooler to further cooling the part of the atmosphere gas; then a step (f) for dehumidifying the part of the atmosphere gas further cooled through the gas cooler to a dew point of -45°C or less in the dryer; then a step (g) for passing the dehumidified part of the atmosphere gas through the low-temperature gas passage of the heat exchanger to increase the temperature of the dehumidified part of the atmosphere gas by heat exchange with a gas in the high-temperature gas passage; and then a step (h) for returning the part of the atmosphere gas having an increased temperature to the heating zone and/or the soaking zone. a step (a) for providing a circulator that includes a heat exchanger for heat exchange between a low-temperature gas and a high-temperature gas, a gas cooler for cooling a gas, and a dryer for dehumidifying a gas to a dew point of - 45°C or less; a step (b) for sucking part of the atmosphere gas from the heating zone and/or the soaking zone; then a step (c) for passing the sucked part of the atmosphere gas through a high-temperature gas passage of the heat exchanger and decreasing the temperature of the sucked part of the atmosphere gas by heat exchange with a gas in a low-temperature gas passage; then a step (d) for mixing the part of the atmosphere gas having a decreased temperature with part of an atmosphere gas sucked from the cooling zone to further decrease the temperature of the part of the atmosphere gas; then a step (e) for passing the part of the atmosphere gas further cooled by mixing with the part of the atmosphere gas sucked from the cooling zone through the gas cooler to further cooling the part of the atmosphere gas; then a step (f) for dehumidifying the part of the atmosphere gas further cooled through the gas cooler to a dew point of -45°C or less in the dryer; then a step (g) for passing the dehumidified part of the atmosphere gas through the low-temperature gas passage of the heat exchanger to increase the temperature of the dehumidified part of the atmosphere gas by heat exchange with a gas in the high-temperature gas passage; and then a step (h) for returning the part of the atmosphere gas having an increased temperature to the heating zone and/or the soaking zone.