A foil bearing , comprising: a stationary side member ; and a rotary side member , any one of the stationary side member and the rotary side member comprising: one or a plurality of top foils formed of a flexible metal thin plate; and an elastic support portion configured to elastically support each of the top foils , a first bearing surface (A) arranged on each of the top foils , a second bearing surface (B) of another member opposed to the first bearing surface (A), an air film formed in a bearing gap (C) between the first bearing surface (A) and the second bearing surface (B) along with rotation of the rotary side member , the rotary side member supported with a pressure of the air film in a non-contact manner, and powder having lubricity and being interposed between the first bearing surface (A) and the second bearing surface (B), characterized in that at least a part of the top foil is elastically deformed in a width direction of the bearing gap (C) in accordance with the pressure of the air film to be shifted alternately between a first state in which a retaining portion capable of retaining the powder is formed in the elastically deformed part of the top foil , and a second state in which the retaining portion substantially disappears, and shifted from the second state to the first state along with an increase in the pressure of the air film, and wherein at least one of the first bearing surface (A) and the second bearing surface (B) includes at least one protruding portion protruding toward the other bearing surface. a stationary side member ; and a rotary side member , any one of the stationary side member and the rotary side member comprising: one or a plurality of top foils formed of a flexible metal thin plate; and an elastic support portion configured to elastically support each of the top foils , one or a plurality of top foils formed of a flexible metal thin plate; and an elastic support portion configured to elastically support each of the top foils , a first bearing surface (A) arranged on each of the top foils , a second bearing surface (B) of another member opposed to the first bearing surface (A), an air film formed in a bearing gap (C) between the first bearing surface (A) and the second bearing surface (B) along with rotation of the rotary side member , the rotary side member supported with a pressure of the air film in a non-contact manner, and powder having lubricity and being interposed between the first bearing surface (A) and the second bearing surface (B), characterized in that at least a part of the top foil is elastically deformed in a width direction of the bearing gap (C) in accordance with the pressure of the air film to be shifted alternately between a first state in which a retaining portion capable of retaining the powder is formed in the elastically deformed part of the top foil , and a second state in which the retaining portion substantially disappears, and shifted from the second state to the first state along with an increase in the pressure of the air film, and wherein at least one of the first bearing surface (A) and the second bearing surface (B) includes at least one protruding portion protruding toward the other bearing surface. <EOS>