We are now developing a Japanese speaking test called SCAT, which is part of J-CAT (Japanese Computerized Adaptive Test), a free online proficiency test for Japanese language learners. In this paper, we focus on the sentence-reading-aloud task and the sentence generation task in SCAT, and propose an automatic scoring method for estimating the overall score of answer speech, which is holistically determined by language teachers according to a rating standard. In that process, teachers carefully consider different factors but do not rate the scores of them. We therefore analyze how each factor contributes to the overall score. The factors are divided into two categories: the quality of speech and the content of speech. The former includes pronunciation and intonation, and the latter representation and vocabulary. We then propose an automatic scoring method based on the analysis. Experimental results confirm that the proposed method gives relatively accurate estimates of the overall score.