PROBLEM TO BE SOLVED: To make a front processor follow unevenness of a field and move up and down and to improve reaping performance of a combine harvester.SOLUTION: Rise and fall operation means of a reaping unit is operated to be switched to a neutral position in which a control valve intercepts an oil path from a hydraulic cylinder to an oil tank to stop the rise and fall of the reaping unit, a lifting position in which the control valve supplies a pressurized oil to the hydraulic cylinder to lift the reaping unit, and a lowering position in which the control valve opens the oil path from the hydraulic cylinder to the oil tank to lower the reaping unit by an empty weight, a free rise and fall control means is equipped in which the control valve opens the oil path from the hydraulic cylinder to the oil tank and maintains the reaping unit in a free rise and fall state when the reaping unit is lowered to a reaping position and the rise and fall operation means is in the neutral position.COPYRIGHT: (C)2011,JPO&INPIT【課題】圃場の凹凸に追随して前処理部を昇降させて、コンバインの刈取性能を向上させる。【解決手段】刈取部の昇降操作手段を、制御弁が油圧シリンダからオイルタンクへの油路を遮断して刈取部の昇降を停止させる中立位置と、制御弁が油圧シリンダに圧油を供給して刈取部を上昇させる上げ位置と、制御弁が油圧シリンダからオイルタンクへの油路を開放して刈取部を自重で下降させる下げ位置とに切換操作自在に構成すると共に、刈取部が下降した刈取位置で、且つ前記昇降操作手段が中立位置の時、制御弁が油圧シリンダからオイルタンクへの油路を開放して刈取部を自由昇降状態に維持制御する自由昇降制御手段を設ける。【選択図】図11
