It is necessary to mention the Zip Code while you send a letter or a parcel via the Japan postal system. The Zip Code numbers literally route the post you send through the geography of Japan to the address given in Kasumigaokamachi, Shinjuku Ku. In fact the actual address is read only at the final post office where they do the final sorting for delivery. Thus Postal or PIN code helps post offices to speed up the sorting and delivery of mails. Zip Code is also otherwise called as Zip Code or PIN code (Postal Index Number).
