An electrically-extendible bicycle includes two shaft tubes, which are arranged symmetrically on opposite sides of a head tube that is set atop a front fork. The two shaft tubes extend through a guide sleeve. The shaft tubes have bottom surfaces on which racks are respectively formed. A motor is set on a rear fork of the bicycle and is coupled to a transmission gear train, which mates the racks on the bottom surfaces of the shaft tubes. After the operation of the motor is activated, the transmission gear train selectively drives forward and backward movement of the shaft tubes so as to extend and retract the bicycle.