A grass mowing machine includes a vehicle body frame, a mower deck incorporating a rotary cutter blade, a coupling mechanism for coupling the mower deck to the vehicle body frame with allowing a lateral displacement of the mower deck in a vehicle body transverse direction, a mower electric motor attached to the mower deck and configured to feed rotary power to the rotary cutter blade and a displacement operation mechanism MV for laterally displacing the mower deck in the vehicle body transverse direction in operative association with the coupling mechanism.