A navigation apparatus is detachably installed to a vehicle and is lockable to implement activation lock of the navigation apparatus. The navigation apparatus stores all of manufacturer serial numbers of wireless IC tags and an ID code. Each IC tag stores the ID code and is attached to a corresponding one of portable items, such as a driver's license, a cellular phone, a wallet and a commutation pass, which are generally used daily. In the navigation system, the manufacturer serial numbers are registered in such a manner that each of manufacturer serial numbers is linked with an icon of a corresponding one of the portable items. When the ID code of the IC tag, which is attached to the corresponding portable item carried by a vehicle occupant, is determined to be valid, the activation lock of the navigation apparatus is released.