The purpose of this paper is to show that South Korean students of Japanese have a gap between their knowledge and usage of Japanese honorifics, and to illustrate misusage of Japanese honorifics by the South Korean students through the analysis of the example sentence, “My father went to the United States.” According to analysis of this paper, native Japanese speakers are influenced by both the UCHI-SOTO relation and the vertical relation of age when they refer to their father. But the students are influenced only by whether “father” is their father or other’s father. Furthermore, the students don’t necessarily recognize the rule in Japanese honorifics, that is, “Do not use the honorifics when you speak of your father to a person outside the family (SOTO).” The conclusion of this paper gives the following suggestive points to the teaching of Japanese honorifics. First, we have to teach that how to refer to “father” varies with the listener. Second, it is required to fully explain the concept of UCHI-SOTO and to make well-known the rule in Japanese honorifics, that is, “Do not use the honorifics when you speak of a person in your group to a person outside your group.”