To lower the will for theft of a thief of a vehicle without provision of an intricate mechanism.

The antitheft sheet 1 is a freely bendable sheet and is made into striking colors, like fluorescent color, yellow and pink. When leaving a bicycle behind, a bicycle owner hangs the antitheft sheet 1 on a rod shaped member such as a handlebar, frame, or spoke of the bicycle. Then, the owner superposes an eyelet 4A and an eyelet 4B and after passing a hook section of a padlock through the eyelet 4A and the eyelet 4B, the owner locks the padlock. Although the bicycle owner can remove the antitheft sheet 1 from the bicycle by unlocking the padlock, the thief cannot unlock the padlock and cannot therefore remove the antitheft sheet from the bicycle. In case the thief steals and rides the bicycle without removing the antitheft sheet, the antitheft sheet attracts people attention and a person riding the bicycle with the antitheft sheet held intact is immediately recognized as the thief.