A motor rotor structure for an electric turbo charger, comprising: a compressor impeller placed in a housing and configured to compress intake air from an air cleaner; a rotor core rotated by a magnetic field formed by a stator placed in the housing; a shaft configured to rotate the compressor impeller and the rotor core together; and a bearing arrangement mounted on a bearing support portion formed in the housing and configured to support the shaft rotatably, wherein the motor rotor structure includes: the rotor core which comprises electromagnetic steel sheets stacked in a thrust direction, which is a direction of the length of the shaft and pre-formed as an integrated member, characterized in that the motor rotor structure further includes: a stopper portion which is formed on the shaft to restrict movement of the rotor core fitted over the shaft in the thrust direction; and a pressing unit which presses the rotor core against the stopper portion, the pressing unit preventing by a pressing force thereof a circumferential phase shift between the shaft and the rotor core, wherein the motor rotor has a pair of bearings, one of which is a first bearing disposed on an outer sleeve fitted over the shaft between the rotor core and the compressor impeller, and the other of which is a second bearing disposed on an opposite side of the rotor core; and the rotor core is pressed by a nut as the pressing unit against the stopper portion via a seal ring sealing a shaft portion and the outer sleeve from a compressor impeller side. a compressor impeller placed in a housing and configured to compress intake air from an air cleaner; a rotor core rotated by a magnetic field formed by a stator placed in the housing; a shaft configured to rotate the compressor impeller and the rotor core together; and a bearing arrangement mounted on a bearing support portion formed in the housing and configured to support the shaft rotatably, wherein the motor rotor structure includes: the rotor core which comprises electromagnetic steel sheets stacked in a thrust direction, which is a direction of the length of the shaft and pre-formed as an integrated member, characterized in that the motor rotor structure further includes: a stopper portion which is formed on the shaft to restrict movement of the rotor core fitted over the shaft in the thrust direction; and a pressing unit which presses the rotor core against the stopper portion, the pressing unit preventing by a pressing force thereof a circumferential phase shift between the shaft and the rotor core, wherein a stopper portion which is formed on the shaft to restrict movement of the rotor core fitted over the shaft in the thrust direction; and a pressing unit which presses the rotor core against the stopper portion, the pressing unit preventing by a pressing force thereof a circumferential phase shift between the shaft and the rotor core, wherein the motor rotor has a pair of bearings, one of which is a first bearing disposed on an outer sleeve fitted over the shaft between the rotor core and the compressor impeller, and the other of which is a second bearing disposed on an opposite side of the rotor core; and the rotor core is pressed by a nut as the pressing unit against the stopper portion via a seal ring sealing a shaft portion and the outer sleeve from a compressor impeller side.