and the third through hole 325 the compression spring 33 is located between the first stopping portion 11723 and the second stopping portion 326 when a force is applied to the operation portion 324 the compression spring 33 is compressed and the engaging member 32 slides along the engaging groove 1172 at this time the second stopping portion 326 moves towards the first stopping portion 11723 to further compress the compression spring 33 and the operation portion 324 is received in the bottom case 11 when the force applied to operation portion 324 is removed the compression spring 33 recovers to expose the operation portion 324 out from the bottom case 11 the tension spring 34 is fixed between the first fixing portion 1173 and the second fixing portion 314 by screws when the first hook 313 engages with the second hook 323 the tension spring 34 is stretched when the first hook 313 detaches from the second hook 323 the tension spring 34 recovers to drive the sliding member 31 towards the pivoting edge 114 to extend the stability plate 40 out of the bottom case 11 the stability plate 40 is secured to the sliding member 31 the stability plate 40 is a substantially rectangular sheet the stability plate 40 includes two third fixing portions 41 and two elastic supporting blocks 42 each third fixing portion 41 includes a plurality of fourth through holes 411 corresponding to the second screw holes 311 and a plurality of positioning posts 412 corresponding to the positioning holes 312 the supporting block.