Hosho-sen (奉書船)

A hosho-sen was a ship carrying not only a shuinjo (license for foreign trade) issued by the Seii Taishogun (literally, "great general who subdues the barbarians") but also a hosho (permit) written by roju (members of shogun's council of elders).

Originally a hosho was a monjo (document), formed by senior vassals or magistrates, in order to certify orders issued by lords were formal and to instruct their prompt execution; in the Muromachi bakufu a hosho was made by kanryo (Shogun's Deputies) together with Shougun's order, the system of which was succeeded by the Edo bakufu.

In the early Edo period, foreign trade was performed by shuinsen carrying a shuinjo (shogunal charter for foreign trade). Hoshosen regulations permitted foreign trade only to ships carrying a hosho countersigned by the roju, in addition to a traditional shuinjo, which was a transitional measure from shuinsen trade to national isolation.

In promoting isolation, a shuinjo, namely a trade permit was an obstacle.
The shuinsen regulations were institutionalized by Ieyasu TOKUGAWA, the first Shogun and many of the shuinjo were issued by Ieyasu himself, so the cancellation of shuinjo was virtually impossible

Therefore, the bakufu, as a means of restricting trade, set a new condition for permitting trade that "both a shuinjo and a hosho should be carried ". That is to say, the bakufu added a collateral condition without canceling the validity of a shuinjo.

In 1633, carrying a hosho was made completely obligatory, leading to the extinction of a shuin-sen system.

Timeline
1601: Ieyasu TOKUGAWA gave notification of shuin-sen trade to other countries. 1631: Hosho-sen regulations came into effect. 1633: Travelling overseas other than by shuin-sen were prohibited. 1634: Overseas trade was restricted. 1635: Travelling overseas and homecoming of Japanese ships were completely banned.