Abstract: A driving device for an electrically driven telescoping cylinder has a motor, a shaft connector, a positioning base and a sensor. The connector is rotatably attached to the motor. The connector includes a driving base, a driven base and a magnet. The driving base is connected to the shaft. The driven base is attached to the driving base and connects with the threaded drive rod of the electrically driven telescoping cylinder. The magnet is mounted around the driving base. The positioning base is mounted in the housing of the electrical cylinder to support the connector. The sensor is secured in the positioning base to detect variations in magnetic field of the magnet. Consequently, the revolutions of the shaft of the motor can be detected. A conventional controller is not needed, and the size of the electrically driven telescoping cylinder can be reduced.