In the present study, we investigated the Word Fluency Functions when reduced Working Memory (WM) capacity and impaired Attention Functions are recognized. We imposed the Japanese version of the reading span test (RST) and 3 types (category, letter, and verb) of word fluency tasks (WFTs) on 14 patients with attention disorder recognized as reduced WM capacity and 28 normal subjects. In the WFTs, 4 trials with a time limit of 60 s were conducted in each condition. The numbers of words generated in the WFTs were compared between the groups, and the correlation coefficient between the proportion of correctly recalled words in the Japanese RST version and the number of words generated in each WFT was calculated. Comparison of the numbers of generated words between the groups resulted in significantly more words by the normal subjects in all 3 conditions. Regarding the correlation between the proportion of correctly recalled words and number of generated words, a positive correlation was observed in the 3 conditions for normal subjects and category and verb conditions for patients with attention disorder. These results reveal that difference in WM capacity exerts influences on word fluency functions of patients with attention disorder. They also indicate that when using the letter fluency task as an assessment battery for fluency functions of patients with attention disorder, we need to fully consider the relationship between fluency and WM functions.