In fifth Meditation, Descartes presents the ontological argument for the existence of God. The ontological argument concludes that the God exists, from the idea of God. And this argument, as it is known well, is first presented by Anselmus, in history of Philosophy. Descartes seems to follow the same form as Anselmus. But in the philosophical works of Descartes, we are faced with problematic situation. For Anselmus conceives the idea of God in objectivity of intellect, but Descartes conceives it in subjectivity of intellect. This difference is not resolved in works of Descartes.
So in order to conceive the property that only Descartes' argument has, we present two questions. First, What is the philosophical setting, that make Descartes conceive the idea of God in subjectivity of 'I'? Second, What is concrete difference between Anselmus and Descartes' argument, that reveals through the philosophical setting? For the difference that is referred above, is staying yet in surface difference. In this treatise, first of all, we will conceive Anselmus' ontological argument and the rejection of Gaunilo, Aquinas and Suarez. And then, we will reveal the property that Descartes' argument has. Through this study, we will reveal Descartes' ontological argument as such.