A vehicle-mounted electronic device according to the present invention is provided with a sensor 15 that detects illumination 17 from a following vehicle 16, in at least one of a display unit 9 and a main body case 7, and is configured such that a control unit 11 rotates the display unit 9 by means of a drive unit 10 when the sensor 15 detects the illumination 17 from the following vehicle 16. Thereby, the illumination 17 from the following vehicle 16 does not reflect on the display unit 9 toward a viewer, as a result of which, the influence by illumination from the following vehicle 16 can be reduced.