This study investigated scope relations between quantifier and focus which are represented in quantified sentences. In the sentence which has both strong quantifier and weak quantifier, one of them has a wide scope and a presuppositional reading, and the other which has a narrow one is interpreted non-presuppositionally. In Korean, when a weak quantifier is separated from VP in surface representation, whether it is a subject or an object, it has only a presuppositional reading. Therefore, there is no scope ambiguity in that sentence. However, when weak quantifier which is an object of transitive verb or a subject of transitive verb is sensitive to focus, it is available to non-presuppositional reading, so that the sentence seems to be ambiguous. Once even weak quantifier out of VP in the Surface structure is focused, it becomes to be in the scope of focus (focal phrase) which is formed in Logical form by a focus projection. And this scope of focus corresponds to a nuclear scope. That is to say, focus operates on the weak quantifier to be interpreted non-presuppositionally in a nuclear scope.