Abstract: A lawn mower has a cutter device which includes lower and upper cutter blades coupled to a rotatable shaft drivable by an engine and substantially horizontally rotatable in a direction. The lower cutter blade has a distal end region including a cutting edge facing in the direction of rotation. The upper cutter blade extends substantially parallel to the lower cutter blade, and has a distal end region including a cutting edge facing in the direction of rotation and positioned forwardly of the cutting edge of the lower cutter blade. The width of the distal end region of the lower cutter blade is larger than the width of the distal end region of the upper cutter blade. The distal end regions of the lower and upper cutter blades extend substantially parallel to each other and are vertically spaced from each other, with an air passage defined therebetween.