A screw pump (2) for feeding highly viscous material such as mixed concrete and the like. Plural projections (4a) engage the helical screw of the screw pumps to facilitating removal of the material such as gravel caught in the screw pump. Further for preventing excessive force from being exerted on the screw because of material caught in the screw pump, a spring is interposed between partitioning plates (5) and hydraulic cylinders (cy) or crank mechanisms. Further, to make the position of the holder (16) for the partitioning plate (5) stable, plural rollers are provided above the holders.