A powdery material feeding device (B1, B2, B3) comprising: a transfer member configured to deliver a powdery material to be discharged; a motor configured to drive the transfer member; and a controller configured to control the motor, characterized in that the controller is configured to selectively conduct constantly keeping control of constantly keeping a manipulated variable without any change for a predetermined period even upon increase or decrease in discharge flow rate of the powdery material, wherein the manipulated variable is one of the rotational speed of the motor, current or voltage applied to the motor, or feedback control of repetitively obtaining a difference between the discharge flow rate of the powdery material and a target value of the discharge flow rate of the powdery material at predetermined cycles and adjusting by increasing or decreasing the manipulated variable at each of the predetermined cycles in order to reduce the difference, wherein the predetermined period for the constantly keeping control is ten times or more the predetermined cycles for the feedback control, the controller is configured to conduct the constantly keeping control immediately after the motor starts, the controller is configured to shift to the feedback control when the difference between the discharge flow rate of the powdery material and the target value of the discharge flow rate of the powdery material has an absolute value less than a threshold after the period for the constantly keeping control elapses, and the controller is configured to conduct constantly keeping control again without shifting to the feedback control when the absolute value of the difference between the discharge flow rate of the powdery material and the target value of the discharge flow rate of the powdery material is more than the threshold after the period for the constantly keeping control elapses, and the manipulated variable during the repeated constantly keeping control is changed in accordance with the difference between the discharge flow rate of the powdery material and the target value of the discharge flow rate of the powdery material after elapse of the period for latest constantly keeping control. a transfer member configured to deliver a powdery material to be discharged; a motor configured to drive the transfer member; and a controller configured to control the motor, characterized in that the controller is configured to selectively conduct constantly keeping control of constantly keeping a manipulated variable without any change for a predetermined period even upon increase or decrease in discharge flow rate of the powdery material, wherein the manipulated variable is one of the rotational speed of the motor, current or voltage applied to the motor, or feedback control of repetitively obtaining a difference between the discharge flow rate of the powdery material and a target value of the discharge flow rate of the powdery material at predetermined cycles and adjusting by increasing or decreasing the manipulated variable at each of the predetermined cycles in order to reduce the difference, wherein constantly keeping control of constantly keeping a manipulated variable without any change for a predetermined period even upon increase or decrease in discharge flow rate of the powdery material, wherein the manipulated variable is one of the rotational speed of the motor, current or voltage applied to the motor, or feedback control of repetitively obtaining a difference between the discharge flow rate of the powdery material and a target value of the discharge flow rate of the powdery material at predetermined cycles and adjusting by increasing or decreasing the manipulated variable at each of the predetermined cycles in order to reduce the difference, wherein the predetermined period for the constantly keeping control is ten times or more the predetermined cycles for the feedback control, the controller is configured to conduct the constantly keeping control immediately after the motor starts, the controller is configured to shift to the feedback control when the difference between the discharge flow rate of the powdery material and the target value of the discharge flow rate of the powdery material has an absolute value less than a threshold after the period for the constantly keeping control elapses, and the controller is configured to conduct constantly keeping control again without shifting to the feedback control when the absolute value of the difference between the discharge flow rate of the powdery material and the target value of the discharge flow rate of the powdery material is more than the threshold after the period for the constantly keeping control elapses, and the manipulated variable during the repeated constantly keeping control is changed in accordance with the difference between the discharge flow rate of the powdery material and the target value of the discharge flow rate of the powdery material after elapse of the period for latest constantly keeping control.