There are only a few studies written about the Choshu War at the end of the Tokugawa period from the view point of political history. The War finally deprived the Bakufu of its influence, and should be recognized as an important event in the political process between 1864 and 1866. It has been generally understood as a war between the Bakufu and Choshu, but one of the major purposes was to punish Choshu as traitors to the imperial court in Kyoto. Therefore, it is necessary to analyze the war as a political affair involving the court, the Bakufu and the clans. In this paper the author analyzes the process of Shogun Tokugawa Iemochi's departure from Edo on June 16, 1865 in order to attack Choshu, for the purpose of viewing the war as the result of contradiction and opposition in the form of government at that time. He conculdes that the Shogun's departure was created by political conflict among the court, the Bakufu and the clans, and also had another purpose to hold a meeting between the Shogun and the Emperor in Kyoto. It was Choshu that legitimized that Shogun'sdeparture. On the other hand, the Hitotsubashi, Aizu and Kuwana clans, which promoted political cooperation between the court and the Bakufu, thought that a meeting between the Shogun and the Emperor would be effective and urgent. They persuaded the court to approve the Shogun's departure meeting with the Emperor in Kyoto. The policy toward the ChoShu would be decided by the form of government. It would also produce a great effect on the Bakufu and the form of government.