A lawn mower comprising: a cutter blade rotatable about a rotation shaft extending in a vertical direction; a drive source configured to drive the cutter blade through the rotation shaft; a grass clippings container configured to store lawn grass cut by the cutter blade and transported by transportation wind generated by the cutter blade, and a grass clippings container weight detection unit configured to detect weight (Wr) of the grass clippings container; characterized by a flap provided for the cutter blade, the flap having a flap angle (θr) changeable along a horizontal line which is perpendicular to the rotation shaft; an actuator configured to control the flap angle (θr) of the flap; a control unit configured to control the actuator; and a travel distance detection unit configured to detect travel distance (Lr) of the lawn mower, wherein the control unit is configured to: implement control in a manner that rotation speed (Ner) of the drive source and the flap angle (θr) of the flap are kept substantially constant over an elapsed time period from time when detection of the travel distance (Lr) is started by the travel distance detection unit to time when travel of predetermined distance (Ls) is completed; determine a change amount (Wa) of the weight (Wr) of the grass clippings container detected by the grass clippings container weight detection unit over the elapsed time period; and implement control in a manner that the rotation speed (Ner) of the drive source and the flap angle (θr) of the flap are adjusted in accordance with the change amount (Wa) of the weight (Wr). a cutter blade rotatable about a rotation shaft extending in a vertical direction; a drive source configured to drive the cutter blade through the rotation shaft; a grass clippings container configured to store lawn grass cut by the cutter blade and transported by transportation wind generated by the cutter blade, and a grass clippings container weight detection unit configured to detect weight (Wr) of the grass clippings container; characterized by a flap provided for the cutter blade, the flap having a flap angle (θr) changeable along a horizontal line which is perpendicular to the rotation shaft; an actuator configured to control the flap angle (θr) of the flap; a control unit configured to control the actuator; and a travel distance detection unit configured to detect travel distance (Lr) of the lawn mower, wherein the control unit is configured to: implement control in a manner that rotation speed (Ner) of the drive source and the flap angle (θr) of the flap are kept substantially constant over an elapsed time period from time when detection of the travel distance (Lr) is started by the travel distance detection unit to time when travel of predetermined distance (Ls) is completed; determine a change amount (Wa) of the weight (Wr) of the grass clippings container detected by the grass clippings container weight detection unit over the elapsed time period; and implement control in a manner that the rotation speed (Ner) of the drive source and the flap angle (θr) of the flap are adjusted in accordance with the change amount (Wa) of the weight (Wr). implement control in a manner that rotation speed (Ner) of the drive source and the flap angle (θr) of the flap are kept substantially constant over an elapsed time period from time when detection of the travel distance (Lr) is started by the travel distance detection unit to time when travel of predetermined distance (Ls) is completed; determine a change amount (Wa) of the weight (Wr) of the grass clippings container detected by the grass clippings container weight detection unit over the elapsed time period; and implement control in a manner that the rotation speed (Ner) of the drive source and the flap angle (θr) of the flap are adjusted in accordance with the change amount (Wa) of the weight (Wr).