In recent syntactic literature, some cases of null arguments observed across languages have been analyzed as the result of argument ellipsis. The main observation of this paper is that the distribution of Japanese AE is systematically constrained with respect to its relative position against wh-phrases. I will propose what I call the 'wh-scope generalization', which states that AE is banned if the ellipsis site is c-commanded by a wh-phrase at LF. It will also be shown that topicalization exhibits exactly the same distribution as AE in terms of its interaction with wh-phrases. Based on these results, I argue that AE induces a topic-related A'-dependency, that is, it involves movement of the target argument to Spec,TopicP.