This paper investigates whether or not Japanese sentences with lexical homonyms cause measurable processing difficulties for Japanese speakers. Pairs of sentences involving lexical homonyms were tested with three types of questionnaires (who-did-what questions, difficulty ratings, and misleadingness ratings) and two experimental tests (an eye-movement monitoring experiment and a self-paced reading experiment). In both the difficulty rating and the misleadingness rating questionnaires, "late boundary" sentences, in which a phrase boundary followed a homonymous phrase, were rated as significantly more difficult and more misleading than "early boundary" sentences, where the boundary preceded the homonymous phrase. The results from the eye-movement study and the self-paced reading study showed that the late boundary difficulties were associated with the processing of the regions that followed the homonymous phrases. These results confirmed our prediction that the difficulty of late boundary sentences is likely to be caused by a subject's original misanalysis and subsequent revision. The results are discussed in terms of possible reasons why the early boundary version was preferred in these sentences.