A compact engine-operated generator unit in which only one centrifugal fan for cooling is provided to restrain generation and leakage of operation noise, while an engine and a generator are still cooled efficiently. Particularly, the engine-operated generator unit comprises an engine and a generator driven by the engine arranged in a direction of a rotary shaft, and soundproof case housing the engine, the generator and other components therein, the generator includes an outer-rotor; a centrifugal fan provided on an end surface the outer-rotor of the generator remote from the engine; a duct covering the centrifugal fan, the generator and the engine and having a suction opening at a side facing the centrifugal fan; a discharge operating on a downstream side of the duct facing an exterior of the soundproof case; and a circulation space provided between the generator and the engine for introducing a part of cooling air flowing toward the engine into the generator to circulate again back to the centrifugal fan.