Predicate-as Parentheticals exhibit word order variability that interacts with contrastive focus placement on the subject or an adjunct phrase. While Culicover and Winkler (2008) discuss that as-clauses share certain properties with other focus inversion construc- tions, a concrete syntactic analysis of Predicate-as clauses has not been provided in the previous studies in order to explain such word order variations as the auxiliary verb cluster phenomenon. This paper proposes that the complicated word order patterns in Predicate-as clauses be accounted for in terms of a constructional constraint for a focus inversion clause, without changing the basic syntactic and semantic analyses of As-Parentheticals. In our analysis, the focus-inversion-clause construction imposes a constraint on the word order domain, so that word order variability needs not to be directly reflected on the constituent structure of the clause.