In the present paper, I will discuss the difficult areas for native speakers of Japanese in learning the pronunciation of English consonants. The difficulties that Japanese speakers encounter when they learn English pronunciation involve the pronunciation of individual phonological segments, which is the segmental component, and word stress, sentence stress, and rhythm, which are considered as suprasegmental components. This paper is limited to the segmental component, especially to English consonants and syllable structure. The subject is examined, first, on the basis of a contrastive analysis of consonants of American English and Japanese, and second, on the basis of how the English segments are perceived and adapted by Japanese speakers according to properties of the system of Japanese phonology, in order to obtain admissible representations.