In human history and after establishing monogamy, a marriage couple who is made up of one man and one woman comes to have absoluteness. As it were, the husband and wife should not make the sentimental or sexual relationship with other people until death at least theoretically. But feeling of love and physical attraction between and among marriage couples weaken by degrees in precess of time, and married people easily chase extramarital relationship. And practically more than 50% of married man had experience sexual intercourse with other women. The contemporary Spanish novelist Juan José Millás already recognized kinds of ‘identity game’ in various ways such as exchange, fragmentation or extension of identity in his works. He descried the couple as like a perfect set and a pair of shoes. He also identified that the his characters in his novel are ones of those people that dream of the extramarital relationship. Despite that, a male character who achieves the extramarital relationship does not feel satisfaction as the result of wish fulfillment. And rather it seems that he solves his desires for extramarital marriage by the change of identity of himself or his partner, or by the projection of the entire group of ‘the woman’ in his partner. Therefore we can suppose that Juan José Millás shows us the possibility of the resolution of that desire by the identity game.