To surely remove burrs near a depth point CP of an inner corner C while preventing a surface of a sheet metal work W from being damaged.

When a burring tool 41 approaches a depth point CP of an inner corner C, an interval between a center of a rotary shaft of the burring tool 41 and an end face of a sheet metal work W is gradually decreased from a predetermined interval d, and burr contact position of a burr removing taper part 49 is gradually changed from a basic end side to a point side, and when the burring tool 41 is separated from the depth point CP of the inner corner C, the interval is gradually increased to be the predetermined interval d, and the burr contact position of the burr removing taper part 49 is gradually changed form the point side to the basic end side.