A flow damper including a cylindrical vortex chamber, a small flow-rate pipe connected to a peripheral plate of the vortex chamber along a tangential direction, a large flow-rate pipe connected to the peripheral plate 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, and a pressure equalization pipe with respective ends being connected to the peripheral plate 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 is arranged with at least a part thereof is located at a higher position than a top plate of the vortex chamber, and an outgassing hole is provided at an uppermost part of the pressure equalization pipe.