A shot processing apparatus (10; 130) comprising a centrifugal projector (20; 21) for projecting projection material onto a workpiece, and a support mechanism for supporting the workpiece at a processing position (18A, 18B, 18C) where the surface treatment can be performed by the projector (20; 21), wherein the projector (20; 21) comprises: a control cage (92; 150; 152; 154; 156; 158) having a cylindrical shape, to the interior of which the projection material is supplied, and on the side wall of which an opening serving as a discharge port for the projection material is formed; and an impeller including multiple blades (104; 190) disposed so as to extend in a radially outward direction of the control cage (92; 150; 152; 154; 156; 158) on the outside of the control cage, and rotating about the central axis of the control cage (92; 150; 152; 154; 156; 158) wherein a rearward inclining portion inclining toward rotationally rearward direction is formed on the rotationally forward surface of the blades (104; 190), characterised in that the shot processing apparatus further comprises a cabinet (12; 132) having a loading/unloading zone for loading/unloading workpieces at an internal upper position, a processing zone for performing surface treatment on the workpiece using projection material projected from the projector (20; 21) at an internal lower position, an inner lid capable of rising and falling between a first position located at upper side of the loading/unloading zone, and a second position located between the loading/unloading zone and the processing zone; and an elevator mechanism for raising and lowering the inner lid so that the inner lid is disposed at the first position when the workpiece is loaded/unloaded from the loading/unloading zone, and the inner lid is disposed at the second position when the workpiece is placed in the processing zone. a control cage (92; 150; 152; 154; 156; 158) having a cylindrical shape, to the interior of which the projection material is supplied, and on the side wall of which an opening serving as a discharge port for the projection material is formed; and an impeller including multiple blades (104; 190) disposed so as to extend in a radially outward direction of the control cage (92; 150; 152; 154; 156; 158) on the outside of the control cage, and rotating about the central axis of the control cage (92; 150; 152; 154; 156; 158) wherein a rearward inclining portion inclining toward rotationally rearward direction is formed on the rotationally forward surface of the blades (104; 190), characterised in that the shot processing apparatus further comprises a cabinet (12; 132) having a loading/unloading zone for loading/unloading workpieces at an internal upper position, a processing zone for performing surface treatment on the workpiece using projection material projected from the projector (20; 21) at an internal lower position, an inner lid capable of rising and falling between a first position located at upper side of the loading/unloading zone, and a second position located between the loading/unloading zone and the processing zone; and an elevator mechanism for raising and lowering the inner lid so that the inner lid is disposed at the first position when the workpiece is loaded/unloaded from the loading/unloading zone, and the inner lid is disposed at the second position when the workpiece is placed in the processing zone.