By employing corpus-based analyses of English-Japanese simultaneous interpretation, we discuss the influence translations have on the working memory load of simultaneous interpreters. To conduct a quantitative analysis with a large corpus, we used the Simultaneous Interpretation Database of Nagoya University. We analyzed a total of 88 sets of simultaneous interpretations of 22 different lectures in English given by 17 interpreters. When the load on the working memory of simultaneous interpreters is increased, the speech time increases, the translation rate decreases, but the average speech rate does not exhibit a relevant change.