A straddled-vehicle authentication system comprising: a power unit control unit configured to control a power unit, the power unit control unit provided in a straddled vehicle, the power unit provided in the straddled vehicle and configured to drive the straddled vehicle; a portable device configured to be used for an authentication to use the straddled vehicle via a wireless communication, the portable device being physically separate from the straddled vehicle; an authentication control unit configured to perform the authentication to use the straddled vehicle by communicating with the portable device, the authentication control unit provided in the straddled vehicle; a main operation part configured to receive an operation for switching the state of the authentication system to at least an OFF state, an authentication verified state, and a power-unit ON state, and to display the state of the authentication system by means of a physical displacement of the main operation part caused by an operation applied to the main operation part, wherein the main operation part is provided in the straddled vehicle, the OFF state is a state in which a power source of the power unit control unit is off and the authentication via the wireless communication between the authentication control unit and the portable device is not performed, the authentication verified state is a state in which the power source of the power unit control unit is off and the authentication via the wireless communication between the authentication control unit and the portable device has been performed, the power-unit ON state is a state in which the power source of the power unit control unit is on and the authentication via the wireless communication between the authentication control unit and the portable device has been performed; and an unauthorized access prevention unit configured to perform a process for preventing an unauthorized access to the straddled vehicle in accordance with at least either one of an elapsed time in the authentication verified state and a status of the authentication performed by the authentication control unit in the authentication verified state. a power unit control unit configured to control a power unit, the power unit control unit provided in a straddled vehicle, the power unit provided in the straddled vehicle and configured to drive the straddled vehicle; a portable device configured to be used for an authentication to use the straddled vehicle via a wireless communication, the portable device being physically separate from the straddled vehicle; an authentication control unit configured to perform the authentication to use the straddled vehicle by communicating with the portable device, the authentication control unit provided in the straddled vehicle; a main operation part configured to receive an operation for switching the state of the authentication system to at least an OFF state, an authentication verified state, and a power-unit ON state, and to display the state of the authentication system by means of a physical displacement of the main operation part caused by an operation applied to the main operation part, wherein the main operation part is provided in the straddled vehicle, the OFF state is a state in which a power source of the power unit control unit is off and the authentication via the wireless communication between the authentication control unit and the portable device is not performed, the authentication verified state is a state in which the power source of the power unit control unit is off and the authentication via the wireless communication between the authentication control unit and the portable device has been performed, the power-unit ON state is a state in which the power source of the power unit control unit is on and the authentication via the wireless communication between the authentication control unit and the portable device has been performed; and the main operation part is provided in the straddled vehicle, the OFF state is a state in which a power source of the power unit control unit is off and the authentication via the wireless communication between the authentication control unit and the portable device is not performed, the authentication verified state is a state in which the power source of the power unit control unit is off and the authentication via the wireless communication between the authentication control unit and the portable device has been performed, the power-unit ON state is a state in which the power source of the power unit control unit is on and the authentication via the wireless communication between the authentication control unit and the portable device has been performed; and an unauthorized access prevention unit configured to perform a process for preventing an unauthorized access to the straddled vehicle in accordance with at least either one of an elapsed time in the authentication verified state and a status of the authentication performed by the authentication control unit in the authentication verified state.