The invention relates to the field of automatic processing equipment, in particular to an automatic nut chamfering device. The automatic nut chamfering device comprises a rack, wherein a supporting plate is arranged on the top of the rack; a material rail which is transversely arranged is arranged on the supporting plate; a positive chamfering mechanism, a turnover mechanism and a negative chamfering mechanism which are sequentially arranged transversely are arranged on positions, beside the material rail, on the supporting plate; a carrying mechanism is arranged on a position, at the other side of the material rail, of the supporting plate; the two ends of the material rail are separately equipped with a charge end and a discharge end; a workpiece enters the material rail from the chargeend; the workpiece is driven to move in a step mode towards the discharge end through the carrying mechanism, and sequentially passes through the positive chamfering mechanism, the turnover mechanismand the negative chamfering mechanism; and positioning mechanisms are arranged on positions, which correspond to the positive chamfering mechanism and the negative chamfering mechanism, below the supporting plate. The automatic nut chamfering device can realize automatic and continuous nut double-sided chamfering operation, and has the advantages of being high in processing efficiency and high inproduction speed.