A vehicle license number recognition system for measuring travel time has been developed. This is a vehicle license number recognition system by applying image processing. A series of four-digit numbers are transmitted to the center. With the recognition results being matched at the center, the system is capable of directly measuring travel time which is an important parameter for the operation of the road traffic surveillance and control system. This paper will discuss (1) a hardware composition for solving problems associated with the imaging processing to be done outdoors and problems such as processing speed, etc.; (2) the method of extracting each letter by extracting license plate region from complicated images, and the letter recognition system based on peripheral-pattern matching; and (3) experiments for evaluation in the field. As a result of experiments for evaluation, the processing time is within a second, and the recognition rate for all moving vehicles has been as high as over 85% at day time and night time.