An information display system (1, 1A, 1B) comprising: an antenna configured to receive outside information from an outside of a vehicle; a display unit configured to double as a high mount stop lamp provided in a rear spoiler of the vehicle and configured to perform display to the outside of the vehicle; and a processing unit capable of executing outside-targeted display processing by which to cause the display unit to perform display associated with the outside information by controlling the display unit based on the outside information received by the antenna; wherein the antenna is configured to receive the outside information from a preceding vehicle traveling in a front side of the vehicle in a vehicle front-rear direction thereof, and the outside information received by the antenna includes alarm information received from the preceding vehicle, the information display system further comprising a housing configured to be installed on the vehicle, the housing including the antenna, the display unit, and the processing unit; wherein the antenna, the display unit, the processing unit, and the housing are embedded in the rear spoiler, and the processing unit, in the outside-targeted display processing, is adapted to control the display unit based on the alarm information received by the antenna, thereby causing the high mount stop lamp to perform alarm display associated with the alarm information different from a display form during braking operation of the vehicle, and change a display form of the high mount stop lamp in accordance with a kind of event signified by the alarm information, wherein the display forms are made different from each other bv applying different features in terms of any of a flashing pattern, a flashing cycle, and a lighting color. an antenna configured to receive outside information from an outside of a vehicle; a display unit configured to double as a high mount stop lamp provided in a rear spoiler of the vehicle and configured to perform display to the outside of the vehicle; and a processing unit capable of executing outside-targeted display processing by which to cause the display unit to perform display associated with the outside information by controlling the display unit based on the outside information received by the antenna; wherein the antenna is configured to receive the outside information from a preceding vehicle traveling in a front side of the vehicle in a vehicle front-rear direction thereof, and the outside information received by the antenna includes alarm information received from the preceding vehicle, the information display system further comprising a housing configured to be installed on the vehicle, the housing including the antenna, the display unit, and the processing unit; wherein the antenna, the display unit, the processing unit, and the housing are embedded in the rear spoiler, and the processing unit, in the outside-targeted display processing, is adapted to control the display unit based on the alarm information received by the antenna, thereby causing the high mount stop lamp to perform alarm display associated with the alarm information different from a display form during braking operation of the vehicle, and change a display form of the high mount stop lamp in accordance with a kind of event signified by the alarm information, wherein the display forms are made different from each other bv applying different features in terms of any of a flashing pattern, a flashing cycle, and a lighting color.