A rotary cutter for a mowing machine includes a cord (4) for mowing grass by rotating, a reel (3) which contains the cord (4) and intermittently rotates to pay out the cord, a case (1) which contains the reel (3), and a cover (2) which covers the case (1), wherein the reel (3) includes an upper cam (3-1) and a lower cam (3-2), a stopper (5) is incorporated in the case (1) at a center of a bottom thereof, one end of the stopper (5) is engaged with the upper cam (3-1) thereby to stop the rotation of the reel (3) , the other end of the stopper (5) is engaged with the lower cam (3-2), one end of the cord (4) is engaged with the stopper (5) from outside thereof and guided out of the rotary cutter through a cord guide (6-1,6-2), and the other end of the cord (4) is guided out of the rotary cutter without touching the stopper (5).