The invention provides a multistage heating system including a compact multistage furnace of which the installation area in a factory is decreased and a work carrier machine. A multistage furnace is configured by piling up a plurality of furnace units in the vertical direction. Each of the furnace units includes an upper heater and a lower heater, support pipes disposed on the upper heater and extending in the horizontal direction, and a plurality of work support bars mounted over the support pipes. A work carrier machine includes work carrier bars extending in the horizontal direction, a horizontal motion mechanism connecting the ends of the work carrier bars and move the work carrier bars on horizontal rails, and a vertical motion mechanism moving the body of the work carrier machine including the horizontal rails on vertical rails.