The invention provides an automatic feeding device of a reinforcement bar straightening machine. The automatic feeding device of the reinforcement bar straightening machine comprises a base, four rubber pads, a supporting column, a feeding tank, a control tank, a display screen, a starting button, a stop button, a main switch, a first switch, a second switch, a third switch, a fourth switch, a holding board, a guide pipe and a groove, wherein the four rubber pads are fixed to four corners below the base; the upper portion of the base is connected with the feeding tank through the supporting column; the control tank is arranged in the middle of the lower portion of the feeding tank; the display screen is installed on one side of the front side face of the control tank; and the starting button and the stop button are sequentially arranged on one side of the display screen. According to the feeding tank, through arrangement of the holding board and the guide pipe, round steel bars are advantageously straightened to pass through the guide pipe and then move forwards linearly into the reinforcement bar straightening machine, damage to the machine is convenient to reduce, and the potential safety hazard that the round steel bars possibly injure pedestrians and operators during paying off is eliminated at the same time.