There is provided a combustible waste injection device and a method for operating the same which can suppress a landing combustion of a combustible waste and suppress excessive change of a flame state from a cement kiln burner even if a rate of using the combustible waste fluctuates. The combustible waste injection device according to the present invention is provided with a combustible waste flow channel which is arranged in an inner side of the air flow channel in an innermost shell, is installed in parallel to an axial direction of the cement kiln burner device and is provided for flow feeding a combustible waste flow, and an assist air inflow port which can flow an assist air flow into the combustible waste flow channel toward an axis center of the combustible waste flow channel in the vicinity of an injection port of the combustible waste flow channel, and the assist air inflow port is arranged at a plurality of positions in relation to a circumferential direction.