Popularizing of Postal Code System 4 Issued on July 1, 1971 (Showa 46) Japan's postal code system was introduced on July 1, 1968 to promote automation of the postal service by adopting automatic reading and sorting machines. The postal codeis assigned to the post office that handles collection and delivery work, and large-scale offices have 3 based on the station order of railway postal transportation routes and routes using the railway network, which was the center of transportation at that time. It was a digit, and 5 digits for other stations. The stamp was issued for the fourth promotion for the purpose of popularizing the zip code, and the number was designed with Mr. Number (zip code character).