An illuminating device for a display device includes a tube lamp which can be driven in parallel by power supplied from a power supply device through a first power supply member and a second power supply member; the first power supply member; and the second power supply member. The illuminating device is provided with illuminating sections whose equivalent circuit is a serially connected body having capacitors connected to the both ends of a negative resistance. The illuminating sections are driven in parallel by separating them into two systems. A voltage to be applied to the left end of the illuminating sections which belong to the first system, and a voltage to be applied to the left end of the illuminating sections which belong to the second system are permitted to be in opposite phases, and a voltage to be applied to the right end of the illuminating sections which belong to the first system and a voltage to be applied to the right end of the illuminating sections which belong to the second system are permitted to be in opposite phases. Thus, display noise of the display device can be reduced.