To provide a flow damper 34 including a cylindrical vortex chamber 35, a small flow-rate pipe connected to a peripheral plate 35C of the vortex chamber 35 along a tangential direction thereof, a large flow-rate pipe connected to the peripheral plate 35C with a predetermined angle with respect to the small flow-rate pipe, an outlet pipe connected to an outlet formed in a central part of the vortex chamber 35, and a pressure equalization pipe 50 with respective ends 50A being connected to the peripheral plate 35C on opposite sides of the outlet and at positions closer to a connection portion between the small flow-rate pipe and the large flow-rate pipe than positions facing each other, putting the outlet therebetween. The pressure equalization pipe 50 is arranged such that at least a part thereof is located at a higher position than a top plate 35A of the vortex chamber 35, and an outgassing hole 51 is provided at an uppermost part 50D of the pressure equalization pipe 50.