Provided is a hydraulic system for a work machine, which can ensure low temperature responsiveness of remote control valves that perform pilot operations of pilot operated directional control valves for controlling hydraulic actuators, respectively. In order to, with bringing an unloading valve V13 to an unloading position 29, circulate oil to a pilot pump oil passage w that supplies the pressure oil from the discharging circuit Y for a pilot pump 19 to remote control valves PV1, PV2, and PV6, a warm-up circuit H that flows the oil from the discharging circuit Y for the pilot pump 19 to a terminal of the pilot pump oil passage w is provided.