A light source control device , comprising: a driver circuit adapted to generate a drive current (lout) that flows in a plurality of semiconductor light sources connected in series; a bypass switch connected in parallel to at least one of the plurality of semiconductor light sources; a main control circuit adapted to cyclically turn on/off the bypass switch in a normal light-up state; a capacitor , wherein a voltage across the capacitor is applied to the main control circuit as an abnormality detection signal (Sdet); and an abnormality detection auxiliary circuit adapted: to change the amount of charge held by the capacitor to a first direction by a first time constant when the bypass switch is off and a voltage between both ends of the bypass switch is lower than a short-circuit detection voltage, or higher than a disconnection detection voltage higher than the short-circuit detection voltage, and to change the amount of charge held by the capacitor to a second direction opposite to the first direction by a second time constant longer than the first time constant when the bypass switch is on, wherein the main control circuit is configured to determine that an abnormality is generated on the basis of the voltage of the abnormality detection signal (Sdet) being higher than a predetermined threshold voltage (Vg), and forcedly turn on the bypass switch . a driver circuit adapted to generate a drive current (lout) that flows in a plurality of semiconductor light sources connected in series; a bypass switch connected in parallel to at least one of the plurality of semiconductor light sources; a main control circuit adapted to cyclically turn on/off the bypass switch in a normal light-up state; a capacitor , wherein a voltage across the capacitor is applied to the main control circuit as an abnormality detection signal (Sdet); and an abnormality detection auxiliary circuit adapted: to change the amount of charge held by the capacitor to a first direction by a first time constant when the bypass switch is off and a voltage between both ends of the bypass switch is lower than a short-circuit detection voltage, or higher than a disconnection detection voltage higher than the short-circuit detection voltage, and to change the amount of charge held by the capacitor to a second direction opposite to the first direction by a second time constant longer than the first time constant when the bypass switch is on, to change the amount of charge held by the capacitor to a first direction by a first time constant when the bypass switch is off and a voltage between both ends of the bypass switch is lower than a short-circuit detection voltage, or higher than a disconnection detection voltage higher than the short-circuit detection voltage, and to change the amount of charge held by the capacitor to a second direction opposite to the first direction by a second time constant longer than the first time constant when the bypass switch is on, wherein the main control circuit is configured to determine that an abnormality is generated on the basis of the voltage of the abnormality detection signal (Sdet) being higher than a predetermined threshold voltage (Vg), and forcedly turn on the bypass switch . <EOS>