A grass mower includes a blade shaft for rotating a blade within a mower deck supported to a vehicle body, a power transmission mechanism for supplying rotational power to the blade shaft, a duct for air-conveying cut grass pieces from the mower deck to the grass collecting bag and a flow boosting device incorporated in the duct. The flow boosting device increases a speed of air flow inside the duct by feeding air through a nozzle opening adjacent an inner circumferential face of the duct along a flow direction of the air flow.
