A supporting device includes a first supporting frame having a first supporting means including a first and a second supporting part, and a second supporting frame having a second supporting means including a third and a fourth supporting part. A supporting passage is defined by the first and the second supporting part. The first and the second supporting means are to support each other. A rail member is to be connected to one of the first and the second supporting frame. The first and the second supporting part are to support the third and the fourth supporting part, respectively. The first supporting frame further includes a first side wall connected to the first and the second supporting part. The first supporting part has a first portion extended from a first end of the first side wall to form a first angle therebetween. The first angle is a non-right angle.