A supporting device for a rail member includes a first supporting frame and a second supporting frame. The first supporting frame has a first supporting means including a first supporting part and a second supporting part. A supporting passage is defined by the first supporting part and the second supporting part. The second supporting frame has a second supporting means including a third supporting part and a fourth supporting part. The first supporting means and the second supporting means are configured to support each other. A rail member is configured to be connected to one of the first supporting frame and the second supporting frame, the first supporting part is configured to support the third supporting part, and the second supporting part is configured to support the fourth supporting part. The first supporting part is spaced from and not directly connected to the second supporting part.