The present study examined how visual working memory affects temporal resolution of visual stimuli that match the memorised nontemporal information about stimulus features (e.g., shapes). The results show that active maintenance of a sample shape in visual working memory impaired the concurrent detection of a sufficiently brief temporal gap within a matching visual target stimulus. The impairment of temporal gap detection was not likely due to the mechanism of visual priming from the presentation of the sample shape, because there was no evidence for priming effects when the sample was only passively viewed without working memory demands or when the sample was initially encoded into memory but did not need to be actively maintained in mind by the time the target stimulus appeared. These findings demonstrate that visual working memory can lower the temporal resolution of visual perception and thereby impair performance in the temporal gap detection task that requires fine temporal segregation of visual information, and they suggest the existence of a previously unknown downside to the interplay between working memory and visual perception.