A seal device (10; 30) that seals between a housing and a rotation shaft passing through the housing, the seal device (10; 30) comprising: a floating ring (15; 35) arranged with a gap (h) with respect to the rotation shaft; a seal portion formed by bringing one end face of the floating ring (15; 35) into contact with the housing; a first axial space (k) between a seal portion opposite side end face of the floating ring (15; 35) and an opposing flange inner wall portion of the housing; and a second axial space (j) provided between the floating ring (15; 35) and the housing, wherein the floating ring (15; 35) includes magnets (12; 32) that contactlessly bias the floating ring (15; 35) to the seal portion via the second axial space (j), the housing is mainly formed by a holder and a flange, wherein the holder has an inner peripheral wall formed in a cylindrical shape, a seal portion side inner wall portion extending from one side of the inner peripheral wall to the radially inside, and a holder seal face connected from the seal portion side inner wall portion to the radially inside, an accommodation portion is formed by surrounding the other side of the inner peripheral wall with the flange, the floating ring (15; 35) is mainly formed by a seal ring and magnets (12; 32) provided in an outer periphery of the seal ring, and the floating ring (15; 35) is accommodated in the accommodation portion, the second axial space (j) is formed between the magnets (12; 32) and the seal portion side inner wall portion, and the seal ring and the holder seal face are closely attached to each other, characterized in that the seal portion side inner wall portion has an outside annular groove portion provided to oppose an outer peripheral face of the magnets (12; 32) and an inside annular groove portion provided to oppose an inner peripheral face of the magnets (12; 32), and a third axial gap (q) between the magnets (12; 32) and a bottom portion of the outside annular groove portion and a bottom portion of the inside annular groove portion is larger than the second axial space (j). a floating ring (15; 35) arranged with a gap (h) with respect to the rotation shaft; a seal portion formed by bringing one end face of the floating ring (15; 35) into contact with the housing; a first axial space (k) between a seal portion opposite side end face of the floating ring (15; 35) and an opposing flange inner wall portion of the housing; and a second axial space (j) provided between the floating ring (15; 35) and the housing, wherein the floating ring (15; 35) includes magnets (12; 32) that contactlessly bias the floating ring (15; 35) to the seal portion via the second axial space (j), the housing is mainly formed by a holder and a flange, wherein the holder has an inner peripheral wall formed in a cylindrical shape, a seal portion side inner wall portion extending from one side of the inner peripheral wall to the radially inside, and a holder seal face connected from the seal portion side inner wall portion to the radially inside, an accommodation portion is formed by surrounding the other side of the inner peripheral wall with the flange, the floating ring (15; 35) is mainly formed by a seal ring and magnets (12; 32) provided in an outer periphery of the seal ring, and the floating ring (15; 35) is accommodated in the accommodation portion, the second axial space (j) is formed between the magnets (12; 32) and the seal portion side inner wall portion, and the seal ring and the holder seal face are closely attached to each other, characterized in that the seal portion side inner wall portion has an outside annular groove portion provided to oppose an outer peripheral face of the magnets (12; 32) and an inside annular groove portion provided to oppose an inner peripheral face of the magnets (12; 32), and a third axial gap (q) between the magnets (12; 32) and a bottom portion of the outside annular groove portion and a bottom portion of the inside annular groove portion is larger than the second axial space (j).