A line-illuminating device comprises a white casing, a bar-shaped light guide housed within the casing, and light-emitting units provided on opposite ends of the bar-shaped light guide. The light-emitting unit has a substrate forming a circuit on which a lead wire for power supply is installed. Formed on a surface of the substrate facing the bar-shaped light guide is a window for coupling in which a green-color light-emitting diode and a blue-color light-emitting diode are installed. Likewise, the light-emitting unit has a substrate on which a lead wire for power supply is installed. Formed on a surface of the substrate facing the bar-shaped light guide is a window for coupling in which two red-color light-emitting diodes are installed.