We investigated distribution of fillers (filled pauses) in the vicinity of boundaries of different strengths in Japanese monologues, to understand whether fillers may convey information about the location and the strength of boundaries. Consistent with the results of studies on Dutch monologues, fillers tend to increase as the boundary strength grows. It has also been revealed that fillers tend to occur phrase-initially, more strongly at deeper boundaries than at shallower ones. Regarding filler types, the frequency of eto grows most sharply as boundary strength increases, as does e to a lesser degree. These findings indicate that occurrence of fillers, particularly phrase-initial eto and e, provide contributory evidence to discourse boundaries.