We propose a new CALL (Computer-Assisted Language Learning) system for non-native learners of Japanese using speech recognition methods. The aim of the system is to help them develop natural pronunciation by automatically detecting their pronunciation errors and then providing effective feedback instruction. An automatic scoring method based on HMM log-likelihood is used to assess their pronunciation. Native speakers' scores are normalized by the mean and standard deviation for each phoneme and are used as threshold values to detect pronunciation errors. Unlike previous CALL systems, we not only detect pronunciation errors but also generate appropriate feedback to improve them. Especially for the feedback of consonants, we propose a novel method based on the classification of the place and manner of articulation. The effectiveness of our system is demonstrated with preliminary trials by several non-native speakers.