A grass mower includes a vehicle speed instruction value calculation section (53) for generating a vehicle speed instruction value including a maximal vehicle speed, based on an operational position of a man-operable vehicle speed controlling tool (15), a mode selection section (70) for selecting a control mode from a plurality of control modes, a control table (52) in which a plurality of control parameters are set, a vehicle speed control target value calculation section (54) configured to calculate a vehicle speed control target value, based on a vehicle speed instruction value generated by the vehicle speed instruction value calculation section (53) and a selected control parameter corresponding to the control mode selected by the mode selection section (70), a cutter blade control target value calculation section (55) configured to calculate a rotational speed control target value for a cutter blade (30), based on the selected control parameter, and a cutter blade control section (4B) configured to contr
