adja to the turn off level for turning off the fluorescent tube 46 a turn off operation then the fluorescent tube 46 a goes out fig8 e in response to the rising edge of the selecting signal optb the signal generating unit 66 d enhances the light volume adjusting signal adjd steeply so that the fluorescent tube 46 d increases in luminance as much as the minimum luminance of the fluorescent tube 46 a fig8 f this prevents the back light 32 b from dropping in luminance due to the turning off of the fluorescent tube 46 a that is the back light 32 b makes little variation in luminance when the fluorescent tube 46 a is turned off subsequently while receiving the selecting signal optb of high level the signal generating unit 66 d outputs to the lighting control circuit 50 b a light volume adjusting signal adjd for adjusting the luminance of the fluorescent tube 46 d so that the luminance gap signal gap decreases consequently the fluorescent tube 46 d decreases in luminance fig8 g with the decreasing luminance of the fluorescent tube 46 d the back light 32 b also decreases in luminance fig8 h at time t 3 the luminance of the fluorescent.