A connecting mechanism (60) is provided for detachably connecting A grass collecting unit (30) to a chassis (4), and the connecting mechanism (60) includes a connecting unit (40) at the grass collecting unit side provided in a support frame assembly (31), and a connecting unit (50) at the vehicle body side provided in the chassis (4). The support frame assembly is vertically movable by the driving unit with the grass container (32) being supported to the ground through a support (70), which selectively achieves a connecting operation performed by the connecting mechanism (60) for connecting the connecting unit (40) at the grass collecting unit side to the connecting unit (50) at the vehicle body side, and a releasing operation performed by the connecting mechanism (60) for releasing connection between the connecting unit (40) at the grass collecting unit side and the connecting unit (50) at the vehicle body side.