A hydraulic system for a working machine includes an fluid cooler including an input port and an output port, the fluid cooler being configured to cool an operation fluid, an outputting portion to output the operation fluid, a traveling hydraulic device to be activated by the operation fluid, an operating hydraulic device to be activated by the operation fluid, a first output fluid tube connecting the operating hydraulic device to a tank, a second output fluid tube branching from the first output fluid tube and being connected to the input port of the fluid cooler, a third output fluid tube connecting the outputting portion to the output port of the fluid cooler, a fourth output fluid tube connected to the traveling hydraulic device, the fourth output fluid tube being connected to the second output fluid tube, and a first check valve disposed on the fourth output fluid tube.