Korea's Japan policy has increasingly become inconsistent and even volatile across time. At the centre of the inconsistency is the Moon Jae-In government's GSOMIA policy. While starting his tenure by deciding to remain in the GSOMIA, the government made 180-degree turn and notified its intention not to renew the agreement when Japan announced export controls. But the decision was completely reversed within months when the government held off ending the agreement. What explains such inconsistency in Korea's Japan policy? To answer this question, the paper proposes a generic model of foreign policy inconsistency, which might be called 'two-level constraint model' and applies it to the case of Korea's GSOMIA policy. The central argument of the model is that the inconsistency in the countries' foreign policy is the result of shifts in foreign policy leaders' incentives, which are affected by the changes in the level of external-and internal political constraints they face. A crucial case study of the Moon Jae-In government's GSOMIA policy finds strong evidence that lends a support for the argument. The paper concludes by offering both a short summary and policy implications.