To accurately and efficiently polish each of a plurality of cutting edges provided at a rotary blade, into fixed shape.

This rotary blade polishing device 8 for a bush cutter polishes the cutting edge 22 provided at each crest part 9b of the rotary blade 9 with crest parts 9b and trough parts 9a alternately formed at the outer peripheral edge. In the device 8, a pedestal 10 is provided with a rotary blade support part 11 for supporting the rotary blade 9 turnably; a polishing machine support base 13; an engaging pin 31 energized toward the outer peripheral edge of the rotary blade 9 and engaged with the trough part 9a; a guide hole 14 for guiding the rotary blade support part 11; and an operating lever 21 for moving the rotary blade support part 11 along the guide hole 14. The guide hole 14 has a polishing guide hole 56 formed to allow the rotary blade support part 11 to move in a direction to engage the trough part 9a with the engaging pin 31 and a direction to disengage it and to allow the rotary blade support part 11 to move into a position where the cutting edge 22 abuts on a polishing surface 4a of a polishing machine 12 in the state of the trough part 9a being engaged with the engaging pin 31.