A manufacturing method of a display device, includes: providing a display module bendable at a bending area and including: a passivation film including a polyimide and disposed both in and outside of the bending area, and an adhesive layer attaching a display panel to the passivation film and including a first adhesive portion in the bending area and a second adhesive portion outside of the bending area; reducing an adhesive force of the first adhesive portion, by irradiating a first laser which is a CO2 laser to the adhesive layer at the bending area, to provide the first adhesive portion which has reduced adhesive force; providing a groove in the passivation film and the adhesive layer, along a boundary of the bending area; and removing the passivation film and the first adhesive portion which has the reduced adhesive force, from the display panel, at the groove.