PURPOSE: To enable the operation of a screw pump to be resumed without any failures by providing a cover body covering a portion of the upper surface side of a screw to automatically reverse the warp of the screw due to sunbeam heat in the stoppage of the screw pump.

CONSTITUTION: A cover body 8 covers a portion 1a of a screw 1 at the opposide directional side to the rotatably driving direction of the screw 1 with respect to the vertical plane X-X passing through the axis of the screw 1. Now, when an exposed portion 1b is heated by direct sun beams P to be thermally expanded, the center of gravity of the screw 1 is moved from positon O1 to O2 on the rotational axis Y-Y to break weight balance of the screw 1 so that the screw 1 is reversed to move its center O2 of gravity to position O3 rigiht below position O1. Namely, the exposed portion 1b is moved to a shaped position where direct sun-beams P are not incident.