The present disclosure relates to a method of cutting a flexible display device, capable of preventing a generation of a defect at the time of cutting the flexible display device, the method including providing a glass mother substrate having a flexible substrate attached thereon and an insulating layer formed on the flexible substrate; melting the flexible substrate and the insulating layer on the mother substrate by irradiating with a first laser beam; and cutting the mother substrate exposed by the irradiation of the first laser beam using a cutting device.