In Japan, malapportionment—the high level of disparity in the size of the population, and thus the weight of votes, across electoral districts—has been a national concern for several decades. Through a review of both normative theories of representation and comparative empirical studies related to the legislative malapportionment, this article identifies two problems in the ways this issue has been addressed in Japan. First, the measurement method used in most Japan-focused studies (the “max-min ratio”) is inappropriate, impeding the effectiveness of reform attempts to date. Alternative measurement methods such as the Loosemore-Hanby index should be used. Second, while most studies adopt a narrow focus in arguing for rectifying malapportionment for the sake of political equality, comparative empirical studies indicate that doing so may lead to other undesirable results such as partisan gerrymandering and lower voter turnout. This article provides a novel and comprehensive framework for possible institutional reforms based on theories of representation.