PURPOSE: To provide a gas collection expansion hood which is simple in its structure and which is securely folded,

CONSTITUTION: A gas collection expansion hood 21 includes a vertically expandable cylindrical hood body 22 and a hood expansion apparatus including a suspension wire mounted on the hood body 22 through a frame 25, a top of which is connected with a duct. The expansion hood 21 includes a plurality of tension rings 27 mounted peripherally on the peripheral surface of the hood body 22 separated vertically, a constriction rope 29 mounted peripherally on the peripheral surface of the hood body 22 so as to constrict the hood body 22 in the middle between the vertically adjacent tension rings 27, and a coupling rope 31 for coupling the vertically adjacent tension rings 27. A suspension wire is mounted on the lower part of the hood body 22 through the frame 22 such that the length of the coupling rope 31 between the vertically adjacent tension rings 27 is shorter than the length of the hood body 22.