The semantic structures of English synonyms (Sorrow, Grief, Sadness; Joy, Pleasure, Delight; .Strength, Power, Force) were compared among the four groups of English- major, English-minor, Native English, and Japanese subjects required to rate the Japanese concepts equivalent to the English ones. The results showed that the semantic structures of the English concepts learned by English-major and English-minor were more similar to those of Japanese group, thus suggesting the existence of a certain mechanism underlying translation which makes the subtle semantic difference in the synonyms insignificant. The effect of familiarity with English on semantic differentiation was partially shown, i.e., the semantic structure of [Sorrow, Grief, Sadness] in English-major was similar to that of Native English speakers.