According to previous theories, effects of repeated exposure of music on pleasingness depend on uncertainty of the music. In this study, "redundancy of rhythm pattern" and "prototypicality of harmony" were manipulated as the factors of uncertainty. The purpose of the following study is to examine effects of repeated exposure on pleasingness determined by the two above mentioned factors. Subjects heard tone sequences that represented four levels of redundancy and four levels of prototypicality, and rated them on 7-point scales of "complexity" and "pleasingness". Pleasingness was shown to be an inverted U-function of redundancy and prototypicality. And then, each tone sequence was repeated and rated pleasingness after each repetition. In a case of sequence whose redundancy caused most pleasingness before repetition, pleasingness of that sequence was decreased by repetition. But, in a case of sequence whose redundancy was too low to cause pleasingness before repetition, pleasingness was seen increased by repetition. On the other hand, pleasingness determined by prototypicality was not affected by repetition, and kept initial pleasingness during repetition.