Working memory characteristics of students with reading difficulties were investigated using 4 types of n-back tasks with different stimuli. The participants, 14 ninth-grade students with reading difficulties and pervasive developmental disorders and 40 students with typical development, were required to judge whether a stimulus was identical to the one that had been shown n before. The results indicated that the students with reading difficulties did not have difficulty at n=0. However, they had difficulty at n=1, if both of the stimuli were numbers or hiragana and kanji characters that required linguistic processing, and with random figures that did not need linguistic processing. The present results suggest that students with reading difficulties may have problems with memory representations that are operated internally. Moreover, it is possible that these students have more fundamental problems, such as attention deficits, which may influence multiple modalities.