An engine-driven work machine system comprising: an engine (3) a work machine (4) driven by the engine (3) a frame (2) supporting the engine (3) and the work machine (4) a sound-insulating housing (6) provided on the frame (2), and housing the engine (3) and the work machine (4), the sound-insulating housing (6) including: a bottom plate (8) a pair of opposing sidewall plates (2b, 2b) extending upward and away from the bottom plate (8) with the engine (3) and the work machine (4) therebetween and a fuel tank (5) connecting upper ends of the sidewall plates (2b, 2b) to each other, characterized in that a mounting flange (5 a) formed around an outer periphery of the fuel tank (5) is superposed on a flat tank-supporting portion (92) formed at the upper ends of the sidewall plates (2b, 2b), a downward4acing collar (95) is formed at an outer end of the mounting flange (5a), an upward-facing collar (102) is formed in the tank-supporting portion (92) and arranged inwardly of the downward-facing collar (95) with respect to the sound-insulating housing (6), and a seal member (96) is provided outwardly of the upward-facing collar (102) with respect to the sound-insulating housing (6) and between the mounting flange (5a) and the tank-supporting portion (92).
