An illuminance distribution response amount as the change amount of the illuminance distribution pattern, associating the position in the irradiation region in the lengthwise direction with the change amount of the illuminance with respect to the change in the drive current, has previously been acquired and stored in a storage unit for each light-emitting block. There is provided an arithmetic processing unit that determines (estimates) a current command value of each of the light-emitting blocks based on a present current command value of each of the light-emitting blocks and the change amount of the illuminance distribution pattern of each light-emitting block in order to bring a present illuminance distribution pattern in the irradiation region in a lengthwise direction close to a target illuminance distribution pattern.