An assembling apparatus of a curtain airbag in a vehicle includes an inflator and an airbag cushion. The airbag cushion includes a body part configured to be unfolded if necessary to protect a passenger, an inlet configured to transmit air from the inflator into the body part, and a first extending part having a predetermined length and extending from the inlet towards the inflator side of the inlet. Also included are at least one bracket on which the inflator is supported and at least one fixed member configured to fix the inflator, enclosing an outside of the inflator.