A cutter blade of a lawn mower includes a blade body and flaps. The blade body includes a shape with a sweepback angle inclined in a reverse-rotation direction of the cutter blade. The flap pivotal axis is provided along a blade edge without intersecting with a blade rotational axis. A flap pivotal axis is provided at a position offset from a line perpendicular to the blade rotational axis and in parallel to the pivotal axis, in a rotation direction of the cutter blade.
