An impeller (16; 55; 60; 70; 90) comprising: a disk (21; 71) that has tubular first and second disk members (26, 27; 73, 75); a blade that is integrally provided with the second disk member (27; 75); and a cover that is integrally provided with the blade and defines a flow passage between the second disk member (27; 75) and the cover , wherein the first disk member (26; 73) defines a part of the flow passage and has a ring-shaped recessed portion (33; 81), that has a central axis direction (X) of the disk (21; 71) as a depth direction (X) thereof, the second disk member (27; 75) has a ring-shaped engaging portion (35; 83) that is configured to engage with the first disk member (26; 73) by being inserted into the recessed portion (33; 81), both the first and second disk members (26, 27; 73, 75) each comprise a through hole , the through-holes being configured such that a rotating body can be inserted into both through-holes ; a first shrink-fitting portion is provided in a boundary portion between an outer circumferential surface (35a; 88b, 89b) of the engaging portion (35; 83) and an inner circumferential surface (33a; 81a, 81b) of the recessed portion (33; 81), the inner circumferential surface (33a; 81a, 81b) coming into contact with the outer circumferential surface (35a; 88b, 89b) of the engaging portion (35; 83), characterized in that the second disk member (27; 75) has a portion abutting against the first disk member (26; 73) in the central axis direction (X) of the disk (21; 71) and a portion forming a gap between the first disk member (26; 73) and the second disk member (27; 75) in the central axis direction (X) of the disk (21; 71). a disk (21; 71) that has tubular first and second disk members (26, 27; 73, 75); a blade that is integrally provided with the second disk member (27; 75); and a cover that is integrally provided with the blade and defines a flow passage between the second disk member (27; 75) and the cover , wherein the first disk member (26; 73) defines a part of the flow passage and has a ring-shaped recessed portion (33; 81), that has a central axis direction (X) of the disk (21; 71) as a depth direction (X) thereof, the second disk member (27; 75) has a ring-shaped engaging portion (35; 83) that is configured to engage with the first disk member (26; 73) by being inserted into the recessed portion (33; 81), both the first and second disk members (26, 27; 73, 75) each comprise a through hole , the through-holes being configured such that a rotating body can be inserted into both through-holes ; a first shrink-fitting portion is provided in a boundary portion between an outer circumferential surface (35a; 88b, 89b) of the engaging portion (35; 83) and an inner circumferential surface (33a; 81a, 81b) of the recessed portion (33; 81), the inner circumferential surface (33a; 81a, 81b) coming into contact with the outer circumferential surface (35a; 88b, 89b) of the engaging portion (35; 83), characterized in that the second disk member (27; 75) has a portion abutting against the first disk member (26; 73) in the central axis direction (X) of the disk (21; 71) and a portion forming a gap between the first disk member (26; 73) and the second disk member (27; 75) in the central axis direction (X) of the disk (21; 71). <EOS>