Provided is a rotary cutter for a mower that achieves easy and rapid cord insertion and improved work efficiency. A rotary cutter for a mower includes: a cord cutting grass or the like; a reel housing the cord, a case and a cover housing the reel therein; a pressing body rotating the reel; and a resilient element elastically supporting the case and the cover, and the rotary cutter is configured such that the reel axially moved by rotation of the pressing body so as to come into contact with the pressing body, and the cord is wound around the reel while being clamped in a clearance created between the reel due to the axial movement of the reel.