This study classified the idiomatic expressions, which were formed with the same vocabulary level, into 4 types, targeting Japanese native learners, and verified on type and its reason for which the subjects feel difficult, through a survey of allowing them to write the literal translation and actual meaning of each idiomatic expression. As a result, the following facts could be known. First, when vocabulary of forming idiomatic expression is corresponded with 1:1 between Japanese idiomatic expressions of indicating the same meaning as Korean idiomatic expression, the recognition level was very high with 96.0%. Second, the recognition level on what some vocabularies of forming idiomatic expression are common accounted just for 54.7%. It is not that the subjects understand certainly by allowing Korean idiomatic expression and Japanese idiomatic expression to be corresponded, but that there was also a case of connecting Korean idiomatic expression with Japanese declinable word. Third, the recognition level when the vocabulary of being formed out of idiomatic expressions just in Korean language is corresponded with Japanese declinable word accounted for 70.7%. Thus, subjects didn't feel so difficult. Fourth, the recognition level on idiomatic expression, which doesn't have idiomatic expression or declinable word of being corresponded in Japanese language, but is semantically described in Korean-Japanese dictionary, accounted for 24.0%, thereby having been indicated very lowly.