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 comprises 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 rotor core has an inner sleeve fitted over the shaft and the plurality of electromagnetic steel sheets which are fitted over the inner sleeve and stacked on one another in a thrust direction of the inner sleeve , and the inner sleeve and the electromagnetic steel sheets are integrally fixed together; wherein the pressing unit presses the inner sleeve , and wherein the bearing arrangement is a ball bearing arrangement and the rotor core has a side surface which is opposed to the ball bearings and which is formed with a flange portion extending radially from an open end peripheral edge of the inner sleeve , and wherein an elastic member is interposed between the flange portion and a bearing of the ball bearing arrangement . 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 comprises 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 rotor core has an inner sleeve fitted over the shaft and the plurality of electromagnetic steel sheets which are fitted over the inner sleeve and stacked on one another in a thrust direction of the inner sleeve , and the inner sleeve and the electromagnetic steel sheets are integrally fixed together; wherein the pressing unit presses the inner sleeve , and wherein the bearing arrangement is a ball bearing arrangement and the rotor core has a side surface which is opposed to the ball bearings and which is formed with a flange portion extending radially from an open end peripheral edge of the inner sleeve , and wherein an elastic member is interposed between the flange portion and a bearing of the ball bearing arrangement . <EOS>