Two experiments were conducted to investigate the cognitive mechanism of shadowing in Japanese. Experiment 1 examined the effects of learners' memory span (including working memory capacity and semantic short-term memory span) and types of sentences on the performances of shadowing in Japanese. Experiment 2 examined the effects of learners' memory span and context in two sentences on the performances of shadowing in Japanese. The main results are as follows: (a) Phonological processing and semantic processing both occur during shadowing, (b) Shadowing where sentences are continuously presented has been observed to be a language activity wherein semantic processing of succeeding sentences is easily affected. Pedagogical implications based on the findings are presented and discussed.