Abstract: For square contingency tables with ordered categories, Iki, Tahata and Tomizawa [12] considered the ridit score type quasi-symmetry model. The present paper proposes an extension of that model having one more parameter. Using the proposed model, the global symmetry model and the marginal mean ridits equality model, this paper also gives a theorem such that the symmetry model holds if and only if these three models hold. Examples are given.