A motor rotor structure for an electric turbo charger is manufactured at low cost with good quality by fixedly fitting, over a shaft, a rotor core having electromagnetic steel sheets pre-formed as an integrated stack. The rotor structure includes a rotor core which is rotated by a magnetic field formed by a stator in a housing; a shaft configured to rotate a compressor impeller and the rotor core together; and a bearing supporting the shaft. The rotor includes the rotor core including the electromagnetic steel sheets; a stopper portion formed at an intermediate portion of the shaft to restrict axial movement of the rotor core; and a pressing unit which presses the rotor core fitted over the shaft against the stopper portion. The pressing unit prevents a circumferential phase shift between the shaft and the rotor core by a pressing force thereof.