Abstract: A pivotal device for connected two parts of a foldable bicycle includes two boards each are connected to a part of the bicycle and are pivotally connected with each other. A clutch device is connected between the two boards and includes two pins extending through the two side plates of each of the two boards. Each of the pins are movable to disengage from one of the two boards to allow the two boards to be pivoted away from each other. A secure device is connected to the clutch device so as to secure the pins of the clutch device in position such that the two boards are not pivoted away from each other.