Japanese learners have insufficient vocabulary knowledge and are likely to encounter unknown words in the comprehension of Japanese sentences. Since inferring the meanings of unfamiliar words contributes to the understanding of the whole sentences, it is considered to be an important strategy in listening comprehension. We investigated the inferring process of unknown words among Chinese learners in an advanced Japanese language class. In the experiment, we used learner's working memory capacity and sentence contextuality as factors. The size of the working memory capacity and the position where the unknown word appears in the sentence (first or second sentence) were set as independent variables. The score and the reaction time of the phonological memory test of unknown words and the comprehension test were measured as dependent variables. The results showed that the Japanese learners put the priority on understanding the meaning of the whole sentence rather than on retaining the phonological information of unknown words in the listening comprehension. Moreover, it became clear that the working memory capacity of the learner could affect the retention of the phonological information of unknown words.