A wireless communication system comprising: an in-vehicle communication device mounted on a vehicle and configured to perform wireless communication with a mobile device; an illuminating device including an illuminating unit, wherein the illuminating device is configured to: acquire, from the in-vehicle communication device, code information; and convert the code information to an optical signal to cause the illuminating unit to blink to thereby transmit the optical signal to the mobile device; and the mobile device that includes a light receiving unit capable of receiving light of the illuminating unit and that is configured to perform the wireless communication with the in-vehicle communication device, wherein the mobile device is configured such that the light receiving unit recognizes the blinking of the illuminating unit and thereby receives the optical signal to acquire the code information characterized in that the illumination unit is configured to illuminate a predetermined area in a vehicle interior of the vehicle; the illumination device further includes an operation switch configured to switch on or off the illuminating unit; the illuminating device is further configured to acquire the code information when a specific operation is performed on the operation switch, wherein the code information is required for establishing the wireless communication with the mobile device, and the mobile device is configured to acquire the code information to establish the wireless communication with the in-vehicle communication device. an in-vehicle communication device mounted on a vehicle and configured to perform wireless communication with a mobile device; an illuminating device including an illuminating unit, wherein the illuminating device is configured to: acquire, from the in-vehicle communication device, code information; and convert the code information to an optical signal to cause the illuminating unit to blink to thereby transmit the optical signal to the mobile device; and acquire, from the in-vehicle communication device, code information; and convert the code information to an optical signal to cause the illuminating unit to blink to thereby transmit the optical signal to the mobile device; and the mobile device that includes a light receiving unit capable of receiving light of the illuminating unit and that is configured to perform the wireless communication with the in-vehicle communication device, wherein the mobile device is configured such that the light receiving unit recognizes the blinking of the illuminating unit and thereby receives the optical signal to acquire the code information characterized in that the illumination unit is configured to illuminate a predetermined area in a vehicle interior of the vehicle; the illumination device further includes an operation switch configured to switch on or off the illuminating unit; the illuminating device is further configured to acquire the code information when a specific operation is performed on the operation switch, wherein the code information is required for establishing the wireless communication with the mobile device, and the mobile device is configured to acquire the code information to establish the wireless communication with the in-vehicle communication device.