To provide a fuel tank for an actuator with an engine capable of enhancing the degree of freedom in the shape of the fuel tank, and of enlarging the fuel tank avoiding the interfering of the fuel tank with an interfering member.

An engine 1 and a generator to be drivingly rotated with the engine 1 driven, are provided, a spark plug cap 14 is projected obliquely upward out of the engine 1. In addition, a fuel tank 20 made out of a synthetic resin is mounted on the engine 1 and the generator so as to be supported thereby, and an avoiding port 31 for the spark plug cap 14 is formed so as to be recessed into a flat roughly circular arc shape in the other side part of the back surface of the fuel tank 20. The manufacture of the fuel tank 20 using synthetic resin such as polyethylene high in density and the like thereby enables the tank to be formed into a complex shape, and also enables the degree of freedom in the shape of the fuel tank 20 to be enhanced to a great extent.