A multifunctional treadmill is provided with a platform on the running deck. A reception cavity is formed on a top of the platform, the reception cavity has a sensor and an operating board tiltably mounted on one side of the reception cavity. When the operating board is released for the reception cavity, the treadmill is in a standard speed mode. When the user wants to exercise and work or do other activities at the same time, the user can store the operating board into the reception cavity so that the operating board and a top surface of the platform become a workbench. Simultaneously, the sensor is triggered and the treadmill changes to a low speed mode. Thus, the safety may be improved by forcefully restricting the speed of the running deck.