The invention discloses a portable machine tool for processing a center hole of a shaft part. The portable machine tool comprises a body, a self-centering three-jaw chuck, a motor, a spindle guide sleeve, a spline sleeve, a drill rod, a drill chuck, a center drillbit, a gear shaft and a hand wheel, wherein the self-centering three-jaw chuck is mounted at the front end of the body, and the motor is mounted at the rear end; the spindle guide sleeve, the spline sleeve, the drill rod, the drill chuck and the center drillbit are mounted in a center hole of the body; the gear shaft is arranged on one side of the spindle guide sleeve; and the hand wheel is arranged at the outer end of the gear shaft. An output shaft of the motor extends into the center hole and is connected with the spline sleeve; the drill rod is sleeved in the front end of the spline sleeve; the spindle guide sleeve is sleeved at the middle part of the drill rod; the front end of the drill rod is connected with the drill chuck; the center drillbit is mounted on the front end surface of the drill chuck; the gear shaft is mounted on the body, located on one side of the spindle guide sleeve and meshed with a rack on the spindle guide sleeve; and the hand wheel is sleeved at the outer end of the gear shaft. The portable machine tool disclosed by the invention has a simple structure and light weight, is easy to operate, and can directly carry equipment to a workpiece as necessary, the workpiece can be mounted on the self-centering three-jaw chuck at the front end of the body and the center of the workpiece can be quickly found; and by rotating the hand wheel, a qualified center hole can be made.