To provide an air blow-up type exhauster for a rectangular vessel efficiently covering generated gas with air curtains even in the rectangular vessel and having no leakage of generated gas in spite of a small quantity of suction air.

The rectangular vessel 2 is formed with the facing long sides A and short sides B being in the relation of A≥B. Both long sides A of the rectangular vessel 2 are provided with blowoff ports 3 for blowing up air along the long sides A, and a hood 4 is provided above the rectangular vessel 2. The air is blown up from the blowoff ports 3, and the air is sucked by the hood 4 to form the air curtains 5 and to lead in outside air 6 from both short side B sides between the air curtains 5. Turbulent flow is not thereby generated even in the rectangular vessel, and the generated gas is efficiently covered with the air curtains to have an effect of no gas leakage in spite of the small quantity of suction air.