The present invention provides a hydraulic circuit for lifting and lowering a reaping part of a combine harvester, which is capable of reducing delay time in lowering the reaping part in a high speed. The solution includes a hydraulic control check valve (11)； a first switching valve (7)； a first orifice (9) connected to the first switching valve in parallel for limiting flow rate of hydraulic oil supplied from a hydraulic pump (4) to a hydraulic cylinder (2)； a resistance valve (10) connected to the first orifice (9) in series for opening the valve when a primary side oil pressure reaches a predetermined pressure； a second orifice (12b) for limiting flow rate of hydraulic oil reversely flowing out from the hydraulic control check valve (11)； a third orifice (18) having a channel cross-section area smaller than that of the second orifice (12b) for limiting flow rate of discharged hydraulic oil； and a second switching valve (19) for selectively switching a hydraulic oil discharge path to a hydraulic oil discharge path passing through the third orifice (18).本發明為提供一種聯合收割機的收割部升降用液壓回路，可縮短使收割部高速下降時產生的時間延遲。其解決方法為具備：液控單向閥(11)；第一切換閥(7)；第一節流孔(9)，與第一切換閥(7)並聯連接，用於限制從液壓泵(4)向液壓缸(2)供給液壓油的流量；阻力閥(10)，與第一節流孔(9)串聯連接，在初級側油壓達到預定壓力時打開閥門；第二節流孔(12b)，用於限制在液控單向閥(11)逆流所排出液壓油的流量；第三節流孔(18)，流路剖面積小於第二節流孔(12b)，用於限制所排出液壓油的流量；及第二切換閥(19)，可選擇地將所排出液壓油的油路切換成通過第三節流孔(18)所排出液壓油的油路。
