In an illumination control apparatus which drives headlamps in a PWM mode and automatically lights them at low power in a vehicle when the DRL executing condition is held, failure in a PWM-drive switching device and break failure in the lamp are detected as well as the arrangement of control units is optimized and meeting models is facilitated. A relay which switches between lamps and a power source, a CPU which is connected to a CAN and drive-controls the relay for manual lighting, and an integrator circuit which integrates voltage of drive side terminals of the lamps are disposed in a main control unit. An FET which switches between the lamps and the power source, a CPU which drive-controls the FET for automatic lighting, and a power source connecting resister having a resistance value greater enough than that of the lamp that drive side terminals of the lamps are connected to the power source through an ignition switch contact of the vehicle are disposed in a DRL control unit. The CPU determines failure based on the output voltage of the integrator circuit.