A rotary cutter for a mowing machine includes a cord for mowing grass by rotating, a reel which contains the cord and intermittently rotates to pay out the cord, a case which contains the reel, and a cover which covers the case, wherein the reel includes an upper cam and a lower cam, a stopper is incorporated in the case at a center of a bottom thereof, one end of the stopper is engaged with the upper cam thereby to stop the rotation of the reel, the other end of the stopper is engaged with the lower cam, one end of the cord is engaged with the stopper from outside thereof and guided out of the rotary cutter through a cord guide, and the other end of the cord is guided out of the rotary cutter without touching the stopper.