PROBLEM TO BE SOLVED: To prevent reduction of control accuracy in draft control caused by chattering.SOLUTION: A tractor includes: a hydraulic lifting/lowering drive unit 17 driving a tillage device to be lifted/lowered； and a mechanical linkage unit 18 for automatic lifting/lowering converting a variation amount of a draft load into a lifting/lowering operation amount to be transmitted to the lifting/lowering drive unit 17 in tillage work. The mechanical linkage unit 18 includes: a load detection member 36 oscillating forward/backward according to the draft load； a biasing mechanism 49 oscillating and biasing the load detection member 36 in a reduction direction of the draft load； an oscillation member 38 supported by the load detection member 36 so as to oscillate； a regulation mechanism 52 regulating oscillation of the oscillation member 38 relative to the load detection member 36； and a link mechanism 34 interlocking and coupling the oscillation member 38 and lifting/lowering drive unit 17. The regulation mechanism 52 includes: a receiver 57 integrally oscillating with the load detection member 36； and a biasing unit 58 oscillating and biasing the oscillation member 38 in a direction to be pressed to the receiver 57.SELECTED DRAWING: Figure 3【課題】チャタリングに起因したドラフト制御における制御精度の低下を防止する。【解決手段】トラクタは、耕耘装置を昇降駆動する油圧式の昇降駆動ユニット１７と、耕耘作業時に牽引負荷の変化量を昇降操作量に変換して昇降駆動ユニット１７に伝える自動昇降用の機械式連係ユニット１８とを備え、機械式連係ユニット１８は、牽引負荷に応じて前後揺動する負荷検出部材３６と、負荷検出部材３６を牽引負荷の低下方向に揺動付勢する付勢機構４９と、負荷検出部材３６に揺動可能に支持された揺動部材３８と、負荷検出部材３６に対する揺動部材３８の揺動を規制する規制機構５２と、揺動部材３８と昇降駆動ユニット１７とを連動連結するリンク機構３４とを備え、規制機構５２は、負荷検出部材３６と一体揺動する受止具５７と、揺動部材３８を受止具５７に押し当てる方向に揺動付勢する付勢ユニット５８とを備えている。【選択図】図３
