In the research to date on government-military relations regarding the Japanese Army, emphasis has been put mainly on the relationship between party cabinets and the military high command. However, during the period between the establishment of a prefectural system to replace Tokugawa period feudal domains and the setting up of an independent general staff office (i.e., during the formation of Japan's modern armed forces), the Army consisted of groups affiliated to the feudal domains, resulting in ambiguity concerning the chain of command. Moreover, in the midst of clear divisions between civilian politicians manning the Cabinet (Sei'in 正院) and military personnel, opinions were divided over how a modern army should be formed; add in the political struggle brewing over the Treasury's jurisdiction over local entities, and there was an eminent danger of the Army disintegrating into smaller factions. Within this situation, the Ministry of the Army was granted broad powers, including control over personnel and military command, and enjoyed relative autonomy from the Cabinet in forming a modern army. However, from 1872-73, during which time the Imperial Guard was reorganized from troops sent by three powerful feudal domains to soldiers from divers regions, a plan was advanced by officers affiliated with Satsuma Domain and Minister of Foreign Affairs Soejima Taneomi 副島種臣 to invade Taiwan, and the Cabinet followed suit with plans of its own to recruit former feudal domain troops to form an expeditionary force. This article interprets these events as a political struggle between the Cabinet and the Ministry of the Army over military authority, and focuses on the participation of the Cabinet's Legislative Bureau (Sa'in 左院) at a time when it was aiming at both the abolition of the feudal status system and constitutional reform. The Legislative Bureau spontaneously cooperated in establishing a military conscription act and approached Tosa Domain with a plan for a "parliamentary body" that would deliberate on military affairs. An examination of this political process makes it possible to reinterpret political-military relations at that time in terms of a triangle involving the Cabinet, the Ministry of the Army and the Legislative Bureau (along with its regional administrators). What ultimately happened was that in June or July of 1873, a group led by councillor (sangi) Itagaki Taisuke of Tosa Domain halted the Legislative Bureau's attempts at constitutional reform by introducing a proposal to invade Korea, which led to political gridlock and the resignation of the invasion supporters in October. This incident should therefore be considered on two levels: constitutional reform vs. centralization of Cabinet power, and the struggle between the Ministry of the Army and the Cabinet over command of the military.