A gas turbine rotor includes a first rotor and a second rotor. The first rotor includes a compressor impeller, a turbine wheel, and a shaft. The turbine wheel has a common rotational axis with the compressor impeller. The shaft connects the compressor impeller to the turbine wheel. The second rotor is an electric generator rotor and defines an inner hollow space. The shaft includes an insertable portion disposed in the inner hollow space of the second rotor.