connecting sleeves 33 and the elastic member 32 is inserted into the receiving space 13 and the pivoting cavities 333 are aligned with the pivoting columns 1331 at this time the connecting sleeves 33 are released and the elastic member 32 repells the connecting sleeves 33 to slide towards the pivoting columns 1331 until the pivoting columns 1331 are rotatably received in the corresponding pivoting cavities 333 then the support board 31 is rotated around the pivoting columns 1331 towards the cover member 20 until the clamp 3121 latches into the clamping slot 1371 at this time the support assembly 30 have been retracted and received in the cover member 20 referring to fig4 to fig7 in use a user can access the operation bar 3122 of the support board 31 by the operation slot 15 to make the clamp 3121 go over the protrusion 137 and out of the clamping slot 1371 then the support board 31 is rotated around the pivoting columns 1331 until the latching portion 3113 latches into the latching slot 134 at this time the latching portion 3113 abuts against a bottom wall of the latching slot 134 and the support board 31 can stably support the portable electronic device 100 upright.