In an engine working machine assembly with a soundproof cover, the soundproof cover is provided for the engine working machine assembly in which a working machine such as a generator, a compressor and the like is adapted to be driven by an internal combustion engine, the working machine and a cooling fan are arranged in order upward above the vertical shaft type air-cooled engine as the internal combustion engine, and a fan case is fixedly secured at its lower wall portion to the engine through a cooling air guide cover for the working machine and a cooling air guide cover for the engine. The soundproof cover comprises an upper side cover section, a front side cover section and a back side cover section. And the upper side cover section is detachably fixed to the fan case at its lower wall portion, at least one of the front side cover section and the back side cover section is detachably fixed to the upper side cover section, and the other cover section is detachably fixed to said one cover section by means of fixing means.