PROBLEM TO BE SOLVED: To effectively prevent winding of grass without increasing air resistance by blades of a cutting blade body.SOLUTION: A bottom of a vertical cutting blade shaft 4 to be driven by a motor M projects downward from a drive case 23, and a cutting blade body 3 is provided under the cutting blade shaft 4. The cutting blade body 3 includes cutting blades 31 provided swingably at a plurality of places in the outer periphery of a support body 3B at intervals in the circumferential direction via cutting blade pins 30, and blades 3C are radially disposed between the cutting blades 31 on the support body 3B. Each blade 3C is extended from inside of the diameter to the outer peripheral part of the support body 3B, and has a grass winding preventive edge Ca rising from the outer periphery of the support body 3B in the outer edge of the diameter to restrain winding of grass to the cutting blade shaft 4. A vent hole Cb is formed in the middle in the radial direction of the blade 3C to permit ventilation of air.
