shaft 239 extending vertically in perpendicular relation to the output shaft 20 the shaft 239 extends downwardly from the gear box 239 through the lower cross member 1e and is connected at its lower end to a two groove pulley 241 having upper and lower grooves of the same diameter belts 242 243 are trained around the pulleys 235 236 respectively and the grooves of the pulley 241 therefore when the output shaft 20 is driven to rotate the pulley 241 is rotated to cause the belts 242 243 and the pulley 235 236 to rotate the cutter blades 233 234 for cutting grass a guide roller 244 is attached to the cutter housing 232 and extends forwardly from one side of the cutter housing 232 for contact with the ground a grass bag 245 is disposed behind the cutter housing 232 for accommodating grass clippings the grass bag 245 is located sideways of the rear wheel 2 behind the side wheel 9 the grass bag 245 is rectangular in shape as seen in plan and has one side 245a positioned just inwardly of the rear wheel 2 and the opposite side 245b positioned directly behind the side wheel 9 and lying flush with or slightly inwardly of the outer side of the side wheel 9 the grass bag 245 has a rear side 245c lying substantially flush with the rear end of the rear wheel 2 the grass bag 245 comprises upper and lower members 246 247 the lower member 247 has a front.