notch 241 of the outer edge portion 24 of the board 2 whereby the board 1 and the board 2 can realize automatic closing or collapse with the elastic members 4 a 4 b in the instant embodiment the elastic members 4 a 4 b comprise elastic bands but they can be replaced by springs or other elastic members in different embodiments further in the instant embodiment two elastic members 4 a 4 b are provided for being attached to the outer edge portion 14 of the board 1 and he outer edge portion 24 of the board 2 yet it is noted that the number of the elastic members 4 a 4 b as mentioned herein is just an illustrative example and modifications of such an illustrative example can be made by for example using a single elastic members 4 a or 4 b that is attached to the outer edge portions 14 24 of the board 1 and the board 2 referring to fig3 the bottom surfaces 12 22 of the board 1 and the board 2 are respectively provided with the plurality of fulcrum stands 5 taking the board 1 as an example for explanation the bottom surface 12 of the board 1 are provided with four fulcrum stands 5 securely fixed thereto among which two fulcrum stands 5 are set at the outer edge portion 14 of the board 1 and are respectively adjacent to the notches 141 of the outer edge portion 14 while the other two fulcrum stands 5 are set at a.