The purpose of this article is to clear up the security relation between Japan and Korea which was formed through dealing the “security crisis” of 1968, which became the origin of the Japan-ROK security cooperation later called “Security Economic Cooperation.” The “security crisis” of 1968 has occurred when reunification by all-out war became impossible due to the establishment of the divided system of the Korean Peninsular. North Korea’s purpose was to bring down South Korea from within by armed guerrilla struggle and achieve the peninsula unity. Therefore, what Korea and Japan emphasized in dealing with this crisis was not how to all-out attack, but rather respond to the indirect aggression, such as guerrilla infiltrations. ROK asked Japan for cooperation concerning the enhancement of equipment of the police engaged in counter guerrilla operations. They have explained Japan that the possibility of an all-out war was low, and that even if war happened to occur, they could respond with the mutual defense treaty with the US. They wanted to respond by strengthening their police equipment and this is why they have requested special assistance from Japan. The Ministry of foreign affairs of Japan and the Prime Minister Sato decided to cooperate to Korea. One reason behind this decision was that they had recognized that ROK was not assuming a conventional war, but just seeking to secure national security by dealing with guerrilla activity. However, ROK ultimately withdrew its request. The pressing issue of drought damage inside the country and the “distrust toward Japan” doubting how willing Japan is toward ROK security, were the cause of the change of ROK’s position. The fact that both countries have discussed and found possible areas of cooperation, and security cooperation has been sought, are significant. Its characteristics are as follows. First, it has clarified the political position of both countries to counter North Korean indirect aggressions. Japan and ROK have shared their perception of the internal security situation problem of ROK due to the indirect aggressions from North Korea, and have inserted the sentence “Ministers of both countries recognize that ROK’s security and prosperity have significant impact on Japanese’s ones” to the Joint Statement at the second Korea-Japan regular ministerial summit. Secondly, in order to ensure the internal security of ROK, Japan and ROK have sought for cooperation to enhance the equipment of the police engaged in counter guerrilla operations. ROK and Japan, while premising on the treaty of alliance with the US, identified new threats from indirect aggressions and tried to find areas of possible cooperation. This has showed the potentiality of security cooperation between Japan and Korea. Thirdly, is the fact that South Korea has ultimately withdrawn the request for police equipment cooperation and eventually switched to a request for emergency economic assistance to focus on domestic stability. This is how a typical pattern of security cooperation between Japan and South Korea, later called “Security Economic Cooperation” has developed.