This paper examined how individual differences in working memory capacity influence processing and comprehension during JSL learner's oral reading task. Word correct per minute of the texts was used as a measure of oral reading fluency. The accuracy in answering yes-no comprehension questions was used as a measure of understanding. Inference skill is measured by accuracy of understanding the word's meaning. The score of reading span test was used as a measure of working memory capacity. 23 Korean speaking Japanese learners participated in the experiment. The result showed that both larger and smaller WM span participants could read texts with equal fluency. On the text understanding, participants with a large WM capacity read texts fluently. At the same time, they could understand the contents of the text and make inferences of the non-semantic information from the texts better than participants with a small WM capacity did. This suggests that individual differences in working memory capacity is a good predictor of reading processing in both oral reading and text understanding as a dual task.