Compound particles are an integrated unit of words that serves as a particle. This paper reveals novel characteristics of toiuno based on the Corpus of Spontaneous Japanese. In particular, (i) the selectional restriction on the compound particle toiuno is much more flexible than the composed counterpart to-iu-no, and (ii) the compound particle toiuno exhibits the ambivalence regarding the "head" and the "bound" status. These structural properties are naturally handled in LFG, with special reference to the DOM(INANT) attribute in line with Falk (2001).