To switch on and off an interio light in accordance with running and stopping so as to eliminate a flicker feeling even by the frequent running and stopping, by setting up a read mode detecting a mean car speed of a vehicle and whether it is running or not and switching on the interior light only in the case of reading a data during stopping.

Through a lamp switch 7 selecting a lighting mode of an interior light 8, the interior light 8 is connected to a control unit 1, in this control unit 1, a mean car speed arithmetic part 9, calculating a mean car speed by information from a car speed sensor 2, is included. The lamp switch 7 is constituted so as to select a mode 2 always lighting by a selector 7a, mode 3 switching on in the case of door opening to be associated with door opening/closing and a mode 4 which is a read mode selecting means switching on at stopping time for data read or the like in the night and switching off at running time. In the case of the made 4, a prescribed mean car speed or less is set as stopping, flicker of the interior light 8 is prevented.