The present invention discloses a license plate image-pickup device and an image exposure adjustment method thereof. The license plate image-pickup device comprises an image-sensing module, a recognition module and a processing module. The license plate image-pickup device takes a scene. The image-sensing module senses the scene to produce an image. The recognition module detects a vehicle object. The processing module adjusts the exposure of the vehicle object to produce an exposure adjusted vehicle object, and then the recognition module detects a license plate object from the exposure adjusted vehicle object, and the processing module adjusts the exposure of the license plate object.