To provide a door opening/closing apparatus which has a gas spring arranged on a lower surface of a roof, wherein gas reaction of the gas spring is boosted without increasing pressure of filler gas or increasing the weight of a rod.

According to the door opening/closing apparatus 11 which has the gas spring 20 arranged on the lower surface of the roof 12A, the gas spring 20 is formed of a cylinder 21, the hollow rod 23 for opening an insertion edge to the cylinder 21 and blocking an opposite edge to the insertion edge, and a piston 26 arranged at the insertion edge to the cylinder 21 of the hollow rod 23. Thus, the interior of the cylinder 21 is partitioned into a piston-side chamber 27 communicating with a hollow portion 23A of the rod 23, and a rod-side chamber 28 enclosing the periphery of the rod 23. The piston 26 is provided with an extension side damping force generating device 35.