1. A hearing aid fitting device, comprising: a database in which a plurality of sets of previously acquired adjustment data obtained by a hearing aid fitting are stored after being classified into a plurality of hierarchical layers of clusters according to the similarity in amount of adjustment, wherein each cluster includes at least one of the sets of previously acquired adjustment data, the clusters of a relatively lower hierarchical layer are within a cluster of a relatively next-higher hierarchical layer, and each cluster at each hierarchical layer has a previously acquired data set that is the representative adjustment data of the cluster; and an adjustment data determination controller that determines adjustment data for a hearing aid by selecting a cluster from among the clusters in each hierarchical layer based on a test sound produced using the representative adjustment data in each cluster.