PURPOSE: To securely prevent vapour from flowing out from a vapour collector by use of a check valve, even when the inside of an underground tank becomes positive as the result of unloading, by providing a check valve preventing the flow to the vapour collector side in a blower for vapour recovery.

CONSTITUTION: The casing 12 of a fluid motor 11 and the casing 22 of a blower 2 1 are jointed to each other through a joint casing 31. And the motor side casing 12 is equipped to an oil feeding pipe S and the blower side casing 22 is equipped to a vapour collecting pipe E respectively. And in the casings 12, 22, respectively a pair of roters 14, 24 are contained to be freely rotatable in a mutually engaged condition in the respective roter chambers 13, 23. In the above construction, a check valve 27 preventing the flow to the upstream is arranged at the opening 22a of the downstream side in the blower side casing 22. When the vapour generated in the underground tank begins to flows out, the vapour is prevented from flowing out in this side of the blower 21 by the function of the check valve.