We examined the modulatory effects of expanding/contracting motion on the capacity of visual short-term memory (VSTM). We used a change detection task in which participants judged whether the orientations of line segments were the same or different between two successively presented displays. We estimated the VSTM capacity based on the accuracy, and compared the capacity for line segments between expanding and contracting motion. As the results, the VSTM capacity for expanding objects was larger than that for contracting objects when the set size was five and seven in experiment 1. Furthermore, the possible account of recency effects of object size were excluded in experiment 2. These results indicated that expanding objects predominantly modulate the capacity of VSTM compared with contracting objects. We discussed these results in terms of possible differences of the expanding/contracting motion processing together with ecological validity.