To provide a vehicular lighting system capable of solving a problem that the brightness of a known vehicular lighting system does not seem to be changed smoothly by human eyes.

The vehicular lighting system comprises a control device 1 and a lamp 2. The control device 1 comprises a luminous flux value setting unit 3 which sets a luminous flux value corresponding to an optical environment around a vehicle and outputs it as a luminous flux value setting signal, a drive signal generation unit 4 which generates and outputs a drive PWM signal of a pulse width based on the luminous flux value setting signal, and generates and outputs the drive PWM signal while a duty ratio is exponentially changed as the luminous flux value set by the luminous flux value setting unit 3 is changed, and a driving unit 5 for supplying power to a light source 11 based on the drive PWM signal. The lamp 2 comprises the light source 11 which radiates the luminous flux of the value set by the luminous flux setting unit 3 based on power from the driving unit 5, and radiates the luminous flux of the exponentially changed value as the luminous flux value set by the luminous flux value setting unit 3 is changed. As a result, the luminous flux seems to be smoothly changed by the human eyes.

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