Engine-driven work machine

The present invention provides an engine-driving working machine. An accommodating engine (3) and a soundproof casing (6) of the generator (4) driven by the engine are arranged on the frame (2), and the soundproof casing is composed of the following components: a baseboard (8); a pair of side wallboards (2b, 2b) which stand from the baseboard; and a fuel tank (5) which connects the top end parts of the side wallboards, in the engine-driving working machine the installing flange (5a) which forms at the periphery of the fuel tank is arranged to a flat fuel tank supporting part (92) that forms onthe top end of a pair of side wallboards, a downward rim (95) forms at the outer end of the installing flange, a upward rim (102) which is arranged nearer to the inner side of the soundproof casing comparing with the downward rim forms at the fuel tank supporting part, and a sealing component (96) is arranged between the installing flange and the fuel tank supporting part at the place which is nearer to the outside of the soundproof casing comparing with the upward rim. Thereby the engine-driving working machine with an excellent sound insulating property and water resistance is provided.