To enhance a position following ability of a work machine operation cylinder and secure a specified finishing accuracy even when excavation load is increased in horizontal leveling work or slope formation work.

A position following feedback control system comprises an operation lever 33, a controller 21, a control valve 36 and feedback groups 43bm, 43st and 43bk from each of angle sensors 16bm, 16st and 16bk of a front linkage or the like. A signal line 51, which is designed to adjust a feedback gain or a feed forward gain, responding to an excavation load, is provide in this control system. The load pressure of a stick cylinder 14st which works mainly for a slope formation work or the like, is detected with a pressure sensor 22st or the like, thereby adjusting increasingly the feedback gain or the feed forward gain by means of a look up table 52, responding to the increase in this cylinder's load pressure. When the excavation load is larger, the attenuation of the front linkage is also great. It is, therefore, possible to protect the control system from being unsteady even when the gain is increased.