In a starting electric motor comprising: a movable pinion cylinder slidably mounted on the extension of the output shaft of the motor, the movable pinion cylinder having the front end portion formed into a pinion part, the rear end portion formed into a clutch inner part of an overrunning clutch, and the middle portion formed into a slidably supporting surface held by a first bearing fitted in the front frame, the shaft extension being supported by the front frame through the movable pinion cylinder, the movable pinion cylinder is slidably and rotatably supported on the shaft extension by a second bearing fixedly fitted in an inner cylindrical wall which is extended in the movable pinion cylinder from the clutch inner part to the middle portion with a gap relatively large between the inner cylindrical wall and the shaft extension.