To feed a lightweight carrying object by a fixed quantity.

In a feed screw conveyor 1, a pair of transfer screws 5 having a screw blade 6 for transferring the lightweight carrying object to the other end from one end, are arranged parallel in a casing having an input port 2 in an upper part on one end, and having a discharge port 3 in a lower part on the other end. A pair of return screws 15 erecting a projection 14 on the outer periphery of a shaft 7 of the transfer screws 5 so as not to check rotation of the transfer screws 5, and so as to project in the radial direction from the screw blade 6, and having a screw blade 16 for transferring the lightweight carrying object in the opposite direction of the pair of transfer screws 5, are arranged above the pair of transfer screws 5. A projection 21 is erected on the outer periphery of a shaft 17 of these return screws 15 so as not to check rotation of the transfer screws 5, and so as to project in the radial direction from the screw blade 17.