A structure is provided for installing in a motorcycle an anti-theft device capable of reporting its position by wirelessly transmitting at least identifying information utilizing the GPS or PHS positioning system. The structure includes a receptacle and an openable cover that can be locked to secure the receptacle, and the anti-theft device is installed in the receptacle. The receptacle can be a helmet box formed in the motorcycle and a cover that can be an openable and lockable motorcycle seat. The structure conceals the anti-theft device, protects it from vibration and invasion of rainwater, and can include a case with enhanced waterproofing capability in which the anti-theft device is accommodated so that an indicator thereof is visible through a transparent window.