To provide a screw conveyor capable of preventing a failure of a device due to objects to be removed and separating the objects to be removed, and a filtration device using an air-driven pump using the screw conveyor and an air-driven pump not using electric power but using air as a power source.

A screw conveyer 5 includes: a conveying passage 51 wherein a mesh type dewatering means 513 to separate objects to be removed from a coolant (a liquid to be treated) containing mixed objects to be removed such as processing waste and sludge is attached in the lower part; and a screw 52 disposed rotationally in the conveying passage 51 to convey the objects to be removed in the liquid to be treated from one side to the other side by means of a spiral blade 521. The screw 52 is equipped with blockage prevention means 523 protruded in the diameter direction beyond the blade 521 and to solve blockage in the dewatering means 513.