A sealing device for sealing an annular gap between a housing made of resin having a stepped shaft hole and a shaft inserted in the shaft hole, the shaft hole having a small diameter portion and a large diameter portion with a diameter larger than that of the small diameter portion, the sealing device to be fitted in a direction from the large diameter portion to the small diameter portion of the housing, the sealing device comprising: at least one sealing member (130, 140); and a case (110; 160; 170; 190) made of metal in which the at least one sealing member (130, 140) is fixed, the case (110; 160; 170; 190) comprising: a cylindrical portion (111; 161; 171), and a flange portion (112; 162; 172; 191) extending to the outer circumferential side from an end of the cylindrical portion (111; 161; 171) and being configured to abut against a step surface between the small diameter portion and the large diameter portion of the housing so that the sealing device is capable to be positioned, characterized in that the at least one sealing member (130, 140) is configured to be slidable on the outer circumferential surface of the shaft; and the case (110; 160; 170; 190) further comprises a tab portion (113; 163; 173; 192) inclining to the outer circumferential side while extending from an end of the flange portion (112; 162; 172; 191) in an axial direction away from the cylindrical portion (111; 161; 171) and having an edge (113a; 163a; 173a) configured to dig into the inner circumferential surface of the large diameter portion of the housing when the tab portion (113; 163; 173; 192) is bent to the inner circumferential side, and the cylindrical portion (111; 161; 171) is configured to be fitted into and to be in contact with the inner circumferential surface of the small diameter portion of the housing. at least one sealing member (130, 140); and a case (110; 160; 170; 190) made of metal in which the at least one sealing member (130, 140) is fixed, the case (110; 160; 170; 190) comprising: a cylindrical portion (111; 161; 171), and a flange portion (112; 162; 172; 191) extending to the outer circumferential side from an end of the cylindrical portion (111; 161; 171) and being configured to abut against a step surface between the small diameter portion and the large diameter portion of the housing so that the sealing device is capable to be positioned, a cylindrical portion (111; 161; 171), and a flange portion (112; 162; 172; 191) extending to the outer circumferential side from an end of the cylindrical portion (111; 161; 171) and being configured to abut against a step surface between the small diameter portion and the large diameter portion of the housing so that the sealing device is capable to be positioned, characterized in that the at least one sealing member (130, 140) is configured to be slidable on the outer circumferential surface of the shaft; and the case (110; 160; 170; 190) further comprises a tab portion (113; 163; 173; 192) inclining to the outer circumferential side while extending from an end of the flange portion (112; 162; 172; 191) in an axial direction away from the cylindrical portion (111; 161; 171) and having an edge (113a; 163a; 173a) configured to dig into the inner circumferential surface of the large diameter portion of the housing when the tab portion (113; 163; 173; 192) is bent to the inner circumferential side, and the cylindrical portion (111; 161; 171) is configured to be fitted into and to be in contact with the inner circumferential surface of the small diameter portion of the housing.