PROBLEM TO BE SOLVED: To inexpensively obtain an unload device of a working machine, which discharges a pressure oil from a hydraulic pump to an unload oil passage by a changeover valve at the stop of hydraulic actuators.SOLUTION: The unload device of the working machine comprises an on-off valve 105 which can switch a state to an opened state that the pressure oil is discharged to the discharge oil passage 104 from a back oil chamber of the changeover valve 102 and a closed state that the discharge of the pressure oil is stopped, and a control valve 107 which switches the on-off valve 105 by pilot hydraulic pressure. When actuator drive circuits 30, 40 are operated for driving the hydraulic actuators 18, 21, the control valve 107 switches the on-off valve 105 to the closed state, and when the actuator drive circuits 30, 40 are operated for stopping the hydraulic actuators 18, 21, the control valve 107 switches the on-off valve 105 to the opened state.COPYRIGHT: (C)2013,JPO&INPIT【課題】油圧アクチュエータの停止時に油圧ポンプからの圧油を切換弁によってアンロード油路に流出させる作業機のアンロード装置を安価に得る。【解決手段】切換弁102の背圧室から排油路104に圧油排出させる開き状態と圧油排出を停止する閉じ状態とに切り換え自在な開閉弁105、開閉弁105をパイロット油圧によって切り換え操作する制御弁107を備えてある。アクチュエータ駆動回路30,40が油圧アクチュエータ18,21を駆動するべく操作されると、制御弁107が開閉弁105を閉じ状態に切り換え操作し、アクチュエータ駆動回路30,40が油圧アクチュエータ18,21を停止するべく操作されると、制御弁107が開閉弁105を開き状態に切り換え操作する。【選択図】図3
