This paper focuses on Sartre's ontology of desire and basic characteristics of his psychanalyse existentielle which is based on the former.His writing on Flaubert L'Idiot de la famille is no doubt an outstanding case of such psychoanalysis.The first is a clarification of his central concept, reflexion, which is different from that of psychology.The opposition is mainly embodied in their completely different understandings of temporality.From this point Sartre's ontology of desire is distinguished from a psychological analysis of desire only as a psychological entity.Through his psychoanalysis, Sartre shows how Flaubert overcame the opposition tetween his basic desire of pour-soi and the laguage as en-soi to have successfully created his own ideal world.As for Deleuze, instead of reflecting on things, which is typical of modernism, philosophers should do creations and experiments; therefore, desire is neighter manqué d'etre nor original totality of pro-ject.Desire is always an experiment in becoming.