A rotation shaft supporting structure for an electric supercharger, comprising: a rotation shaft to which a compressor wheel is attached, the compressor wheel being a wheel of a supercharging side; an electric motor comprising a motor rotator securely installed to the rotation shaft, and a stator for applying torque to the motor rotator; a bearing for supporting the rotation shaft, the bearing being provided on a bearing side closer to the compressor wheel than the motor rotator; and a damper unit for absorbing shaft vibration of the rotation shaft, the damper unit being provided at a shaft end on an opposite side to the bearing side, characterized in that the damper unit comprises: a roller bearing provided around the rotation shaft, the roller bearing being a grease-filled roller bearing that is filled with grease; a damper provided around an outer periphery of the roller bearing; a ring-shaped member provided around an outer periphery of the damper, wherein the damper is an oil film damper formed by a pair of seals provided in two ends of the roller bearing in the axial direction of the rotation shaft along the outer periphery of the roller bearing and an oil enclosure part enclosing oil in a ring-shaped space surrounded by the pair of seals, an inner periphery of the ring-shaped member and the outer periphery of the roller bearing. a rotation shaft to which a compressor wheel is attached, the compressor wheel being a wheel of a supercharging side; an electric motor comprising a motor rotator securely installed to the rotation shaft, and a stator for applying torque to the motor rotator; a bearing for supporting the rotation shaft, the bearing being provided on a bearing side closer to the compressor wheel than the motor rotator; and a damper unit for absorbing shaft vibration of the rotation shaft, the damper unit being provided at a shaft end on an opposite side to the bearing side, characterized in that the damper unit comprises: a roller bearing provided around the rotation shaft, the roller bearing being a grease-filled roller bearing that is filled with grease; a damper provided around an outer periphery of the roller bearing; a ring-shaped member provided around an outer periphery of the damper, wherein the damper is an oil film damper formed by a pair of seals provided in two ends of the roller bearing in the axial direction of the rotation shaft along the outer periphery of the roller bearing and an oil enclosure part enclosing oil in a ring-shaped space surrounded by the pair of seals, an inner periphery of the ring-shaped member and the outer periphery of the roller bearing. a roller bearing provided around the rotation shaft, the roller bearing being a grease-filled roller bearing that is filled with grease; a damper provided around an outer periphery of the roller bearing; a ring-shaped member provided around an outer periphery of the damper, wherein the damper is an oil film damper formed by a pair of seals provided in two ends of the roller bearing in the axial direction of the rotation shaft along the outer periphery of the roller bearing and an oil enclosure part enclosing oil in a ring-shaped space surrounded by the pair of seals, an inner periphery of the ring-shaped member and the outer periphery of the roller bearing.