A cooling device includes a conveying portion configured to convey a sheet while holding the sheet between a first belt and a second belt; a stretching roller configured to drive the first belt inside the first belt; and a cooling portion having a flow-passage forming portion for forming a flow passage of a cooling medium and configured to cool the sheet through the first belt. The sheet includes a first vertical rib that extends in a first direction and protrudes in a second direction out of the plane. A standard pull-chain assembly is used to articulate the ball valve between its open position and its closed position.