The 1:1 and 1:2 macroscopic binding constants of didecyldimethylammonium bromide (DDAB) and alpha-, beta-, and gamma-cyclodextrins (CD) are determined from the electromotive force measurements with a DDAB-selective electrode, and the magnitude of these constants is interpreted in terms of the molecular structures of complexes. The 1:1 macroscopic binding constants of a double chain surfactant is 2-fold larger than that of a single chain, because the former has two chains. The 1:1 macroscopic binding constants of DDAB are in the increasing order alpha-CD < beta-CD approximate to alpha-CD, consistent with those of a single chain surfactant. In the 1:1 complex of DDAB and gamma-CD, one or two decyl chains are incorporated into the CD cavity. The 1:2 macroscopic binding constants of DDAB are in increasing order gamma-CD << beta-CD alpha-CD. This order is interpreted in terms of the structure of complexes: the first larger ligated CD inhibits the second ligation more strongly. The present result serves for the quantitative understanding of the interaction between membrane phospholipid and CD as well as the structure-complexation relationship.