Many primate species eat mushrooms, and Japanese macaques in Yakushima (Macaca fuscata yakui) are known to become strongly mycophagous depending on the season. We carried out behavioral observation and sample collection in Yakushima, where fungal diversity is expected high. Our research interests lie in whether they would avoid poisonous mushrooms and select “edible” mushrooms, and how they make their decision. The most intense mycophagy was observed from late June to early August, in accordance with fungal fruiting. Our research shows that the macaques consume a considerably various mushrooms although they account for only small proportion of the annual dietary composition. We found that the macaques, to some degree, discriminate poisonous mushrooms using examining behaviors based on previous knowledge and that they do not selectively eat “edible” mushrooms. Our research suggests that the macaques treat Amanita differently; more specifically they often reject Amanita after sniffing or nibbling. Macaques, therefore, might have a certain image of mushrooms, at least at the genus level, and change their feeding behaviors.