The invention relates to an anti-theft device for windsurfing boards, which are made to engage with the profile groove thereof for fin or mast groove. The anti-theft device is composed of a handle and plug-in part and of a locking element which engages into the undercut of the profile groove. In order to correspond to requirements for vastly different overall lengths, the locking element is configured as a turning plate with angled-off border pieces of different lengths which are used by rotating or turning.
