An object is to provide a seal structure capable of reducing abrasion of a seal ring without increasing the number of components and of minimizing generation of abrasion powder. A seal structure to seal clearance between an outer peripheral surface 8a of a rotary shaft 8 and an inner peripheral surface 6a of a bearing housing 6 includes: a first seal groove 22A formed on the outer peripheral surface 8a of the rotary shaft 8; a second seal groove 22B disposed between the first seal groove and the impeller; a first seal ring 26 to be mounted to the first seal groove; and a second seal ring 28 to be mounted to the second seal groove. The first seal ring 26 includes a first-seal body portion 26A mounted to the first seal groove, and a first-seal protruding portion 26B protruding from the first-seal body portion toward the second seal ring 28, and being configured to be in contact with the second seal ring contacting a bearing-side wall surface 22Ba of the second seal groove, in a state in which the first-seal body portion is in contact with a bearing-side wall surface 22Aa of the first seal groove.