An engine-driven work machine system includes an engine; a work machine driven by the engine; a frame supporting the engine and the work machine; and a sound-insulating housing provided on the frame. The sound-insulating housing includes a bottom plate; a pair of opposing sidewall plates extending from the bottom plate with the engine and the work machine therebetween; and a fuel tank connecting upper ends of the sidewall plates. A mounting flange formed around an outer periphery of the fuel tank is superposed on a flat tank-supporting portion formed at the upper ends of the sidewall plates. A downward-facing collar is formed at an outer end of the mounting flange. An upward-facing collar is formed in the tank-supporting portion and arranged inwardly of the downward-facing collar with respect to the sound-insulating housing. A seal member is provided outwardly of the upward-facing collar and between the mounting flange and tank-supporting portion.