A door is formed into a folding door by dividing the door into two parts to left and right, that is, a hanging door and a door-end door pivotally supported by the hanging door, and the door-end door is used as the pressure difference mitigating mechanism, and the two doors are integrally operated in a normal time, while if a pressure difference is generated, the door-end door can be first opened in order to reduce an opening force, and the door device with a pressure difference mitigating mechanism with excellent operability is provided.A handle position, a latch position, and a torque are adjusted for a handle for door opening/closing, a door closer, a hinge closer for rotating the door-end door with respect to the hanging door, a latch A of the door-end door to a door frame, and a latch B of the door-end door to the hanging door.