A change-over apparatus for cooling a gas passage is provided with a cooling chamber and a gas cooling and circulating system. The apparatus is further provided with a stationary partition plate and a slidable shield plate. The stationary partition plate has a suction opening and a discharge opening which are independently communicated respectively with a suction port and a discharge port, and the slidable shield plate has a shield part for partially shielding the suction opening and the discharge opening, whereby it is possible to alternately change over the direction of the gas passing through the cooling chamber.
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