Perceived prominence as a function of fundamental frequency (f0) is examined with special attention given to downstep in Standard Japanese, a lowered f0 of the material following an accented word compared with that following an unaccented word. This lowering does not signal a reduction in prominence, whereas f0 compression triggered by focus is associated with prominence. The purpose of this study is to investigate how much f0 lowering is perceived as equally prominent to understand a perceptually acceptable pitch range of Japanese downstep. A prominence perception test was conducted with varying peak f0s of two successive phrases. Results of the test reveal that there is a particular f0 level of the following phrase to be perceived as equally prominent as the preceding phrase, regardless of the peak f0 of the preceding phrase. This result indicates that f0 differences between the preceding and the following phrases are greater as the f0 of the preceding phrase increases, corroborating the effect of f0 on prominence perception found in the literature. Furthermore, an interesting asymmetry is suggested between production and perception of downstep in Japanese.