2 so as to fix it at a definite location then the adjacent sides of the frame 7 are movably connected together by means of binding members 71 to make the frame 7 collapsible as shown in fig2 additionally the frame 7 has an open side 72 at opposite ends for the inflated air chamber 2 to expand out therethrough the frame 7 is provided with a plurality of hooks 73 at the bottom to engage with the hook rings 74 which are fixed and somewhat hidden on the ground so as to stably keep the frame 7 in place with the hook rings 74 not protruding out of the ground the frame 7 is further formed with an air chamber space 75 in the interior for receiving the air chamber 2 in using as shown in fig2 the air chamber 2 is deposited in the air chamber space 75 of the frame 7 and then the air chamber 2 is filled up with air to become inflated and forced to move toward the opposite open sides 72 of the frame 7 as the size of the inflated air chamber 2 is a little larger than the air chamber space 75 the.