The study's purpose was to clarify the developmental characteristics of working memory in hard of hearing children on the basis of language ability and task variables. Eighty-three congenitally severely hard of hearing children in grades 3-9 attending Japanese elementary and junior high school were aggregated on the basis of grade and language ability into six groups and received verbal and nonverbal tasks to measure their working memory capacity. The results suggest that hard of hearing children's nonverbal working memory is less affected by language ability and develops slowly as the school year progresses, showing a developmental trend similar to that of hearing children. Verbal working memory showed differences between groups by language ability in all grades due to the influence of language ability underlying processing in the phonological loop, but the results suggest that significant improvement occurs during elementary school regardless of language ability.