To automatically polish even a comparatively large workpiece by unnecessitating an extension tube for changing an injecting direction of abrasive grain, simplifying its structure, saving on space of a device, and automatically oscillating an injection nozzle in a fixed range.

This injecting device 10 is constituted of an emitting unit 30 rotating an impeller constituted by holding a plurality of blades by two sheets of discs and opening a peripheral surface between the blades by winding a rotary belt for closing a part of the peripheral surface on the impeller and provided with a nozzle for injecting abrasive grain in a tangential direction of the discs passing a separation point of the peripheral surface of the impeller and the rotary belt, and an angle adjusting substrate 20 for rotatably supporting the whole of the emitting unit 30 independently from rotation of the impeller. The emitting unit 30 may be rotated by a motor for rotating and driving the angle adjusting substrate 20. A means for providing a rotary shaft of the impeller in the emitting unit 30 at a center of the angle adjusting substrate 20 is selectively used.