A lawn-grass mowing machine, comprising a collector (32) which contains lawn-grass mowed with a mower (5), characterized in that the lawn-grass mowing machine comprises: an introducing guide (70) provided inside the collector (32), which receives mowed-grass; a diffusion guiding plate (73) arranged at one end side of the introducing guide (70); a bracket member (71) fixed to the introducing guide (70); and a fulcrum shaft (72) held by the bracket member (71), wherein the diffusion guiding plate (73) is held by the fulcrum shaft (72), and the diffusion guiding plate (73) is configured so as to be swingable.