PROBLEM TO BE SOLVED: To prevent lowering a working device caused by leakage of oil at a spool valve while simplifying its constitution and reducing costs.SOLUTION: In the hydraulic control structure for lifting and lowering a working implement including a spool valve 28 for regulating the flow of oil to a hydraulic actuator of lifting and lowering the working device based on the operation of a lifting lever 14, and a hydraulic lock valve for opening and closing a supply/discharge oil path extending from the hydraulic actuator 2 to the spool valve 28, the hydraulic lock valve has an opening/closing valve configured to couple the lifting lever 14 and the opening/closing valve through a coupling member 56 to be mechanically associated so that the opening/closing valve closes the supply/discharge oil path in association with the operation of the lifting lever 14 to a neutral position and the opening/closing valve opens the supply/discharge oil path in association with the operation of the lifting lever 14 from the neutral position to another position.COPYRIGHT: (C)2012,JPO&INPIT【課題】構成の簡素化やコストの削減を図りながらスプール弁でのオイルのリークに起因した作業装置の下降を防止する。【解決手段】昇降レバー14の操作に基づいて作業装置昇降用の油圧アクチュエータに対するオイルの流れを制御するスプール弁28と、油圧アクチュエータ2とスプール弁28とにわたる給排油路を開閉する油圧ロック弁とを備えた作業機の昇降用油圧制御構造において、油圧ロック弁を開閉弁で構成し、昇降レバー14の中立位置への操作に連動して開閉弁が給排油路を閉じ、昇降レバー14の中立位置から他の操作位置への操作に連動して開閉弁が給排油路を開くように、昇降レバー14と開閉弁とを連係部材56を介して機械的に連動可能に連係する。【選択図】図7
