A lighting system for illuminating an interior of a vehicle having seats (7, 9, 11), wherein the seats each have a slide position along a respective range in a front-back direction, the system comprising: a main control unit and reading lamps (25, 27, 29, 31), each reading lamp corresponding to a seat and having a load control unit, wherein the main control unit is configured to receive slide position data of the seats from a seat control unit and to transmit control signals for controlling light sources based on the slide position data of the seats (7, 9, 11) through a multiplex communication line; and each load control unit is for controlling driving of a respective plurality of loads (33a - 33d) based on the control signals, each load control unit comprising: a single substrate; the loads (33a - 33d) implemented on the substrate; and a controller-built-in connector comprising a connector part to which a corresponding connector part of the multiplex communication line is connected, and a controller built in the controller-built-in connector, the controller-built-in connector mounted on the substrate and to which the respective loads (33a - 33d) are connected through a circuit pattern of the substrate electrically, wherein the controller is configured to control the driving of the respective loads (33a - 33b) based on the control signals which are inputted to the controller through the multiplex communication line connected to the connector part, the loads (33a - 33d) are LED chips as light sources for illuminating an interior of the vehicle and are arranged at intervals, to be in the front-back direction when arranged in the vehicle, so as to sharingly cover the slide range of the seat (7, 9, 11) corresponding to the reading lamp, and the controller is configured to control lighting of the LED chips. a main control unit and reading lamps (25, 27, 29, 31), each reading lamp corresponding to a seat and having a load control unit, wherein the main control unit is configured to receive slide position data of the seats from a seat control unit and to transmit control signals for controlling light sources based on the slide position data of the seats (7, 9, 11) through a multiplex communication line; and each load control unit is for controlling driving of a respective plurality of loads (33a - 33d) based on the control signals, each load control unit comprising: a single substrate; the loads (33a - 33d) implemented on the substrate; and a controller-built-in connector comprising a connector part to which a corresponding connector part of the multiplex communication line is connected, and a controller built in the controller-built-in connector, the controller-built-in connector mounted on the substrate and to which the respective loads (33a - 33d) are connected through a circuit pattern of the substrate electrically, wherein the controller is configured to control the driving of the respective loads (33a - 33b) based on the control signals which are inputted to the controller through the multiplex communication line connected to the connector part, the loads (33a - 33d) are LED chips as light sources for illuminating an interior of the vehicle and are arranged at intervals, to be in the front-back direction when arranged in the vehicle, so as to sharingly cover the slide range of the seat (7, 9, 11) corresponding to the reading lamp, and the controller is configured to control lighting of the LED chips. a single substrate; the loads (33a - 33d) implemented on the substrate; and a controller-built-in connector comprising a connector part to which a corresponding connector part of the multiplex communication line is connected, and a controller built in the controller-built-in connector, the controller-built-in connector mounted on the substrate and to which the respective loads (33a - 33d) are connected through a circuit pattern of the substrate electrically, wherein the controller is configured to control the driving of the respective loads (33a - 33b) based on the control signals which are inputted to the controller through the multiplex communication line connected to the connector part, the loads (33a - 33d) are LED chips as light sources for illuminating an interior of the vehicle and are arranged at intervals, to be in the front-back direction when arranged in the vehicle, so as to sharingly cover the slide range of the seat (7, 9, 11) corresponding to the reading lamp, and the controller is configured to control lighting of the LED chips.