A method of fabricating a flexible display device is to prevent damage due to a defective detachment of an auxiliary substrate by carrying out the detachment in a manner of irradiating lasers onto a sacrifice layer interposed between a flexible substrate and an auxiliary substrate and thereafter taking away a vacuum by injecting air into the interface between the flexible substrate and the auxiliary substrate. The fabricating method includes providing an auxiliary substrate, forming a sacrifice layer on the auxiliary substrate, forming a flexible substrate on the auxiliary substrate with the sacrifice layer formed thereon, forming a display panel on the flexible substrate, removing the sacrifice layer interposed between the flexible substrate and the auxiliary substrate by way of a laser irradiation, injecting air between the flexible substrate and the auxiliary substrate removed the sacrifice layer therebetween, and detaching the auxiliary substrate from the flexible substrate.