This study examined the cognitive mechanism of shadowing in Japanese as a second language for an intermediate and an advanced class of Japanese learners. The concrete aim of this study is to sift concurrency phonological processing and semantic processing during shadowing. Just after shadowing of 2 sentences, the participants were asked to evaluate the semantic plausibility of the first sentence or the second. The main results were as follows: (a) the rate of correct answer of evaluating the semantic plausibility in the larger-memory span group was higher than that of the smaller-memory span group, (b) memory capacity has no influence on the reaction time and the shadowing time. These results suggested that the learners of larger-span of memory was doing the cognitive processing concerning the understanding of the content of the model sentence during shadowing. On the other hand, as for the learners of smaller-span of memory, it seems that semantic processing about the sentence was inadequate.