An apparatus with a seal (1,101,201,301), which seals lubricant between two members that rotate relative to each other, the apparatus (1,101,201,301) comprising: a first member having a circular hole; a second member passing through the circular hole and configured to rotate relative to the first member; a main oil seal sealing the lubricant and being inserted between an inner circumferential surface of the circular hole and the second member; a secondary oil seal movable along a center line of the circular hole and positioned on an opposite side of the lubricant, the main oil seal being interposed therebetween; a dust seal (22,242,342) positioned on an opposite side of the lubricant, the secondary oil seal being interposed therebetween; wherein a groove (38,138,238,338) encircling in a circumferential direction is formed on one of the inner circumferential surface of the circular hole and an outer circumferential surface of the second member, and the groove (38,138,238,338) is positioned on the opposite side of the lubricant, the main oil seal being interposed therebetween, the secondary oil seal is movable from a reserve position, at which position the secondary oil seal opposes the groove (38,138,238,338) and does not contact the member that is formed with the groove (38,138,238,338), to a sealing position, at which position the secondary oil seal does not oppose the groove (38,138,238,338) and contacts the member that is formed with the groove (38,138,238,338), and the dust seal (22,242,342) is coupled to one of the first member and the second member and contacts another of the first member and the second member without opposing the groove both when the secondary oil seal is positioned at the reserve position and when the secondary oil seal is positioned at the sealing position. a first member having a circular hole; a second member passing through the circular hole and configured to rotate relative to the first member; a main oil seal sealing the lubricant and being inserted between an inner circumferential surface of the circular hole and the second member; a secondary oil seal movable along a center line of the circular hole and positioned on an opposite side of the lubricant, the main oil seal being interposed therebetween; a dust seal (22,242,342) positioned on an opposite side of the lubricant, the secondary oil seal being interposed therebetween; wherein a groove (38,138,238,338) encircling in a circumferential direction is formed on one of the inner circumferential surface of the circular hole and an outer circumferential surface of the second member, and the groove (38,138,238,338) is positioned on the opposite side of the lubricant, the main oil seal being interposed therebetween, the secondary oil seal is movable from a reserve position, at which position the secondary oil seal opposes the groove (38,138,238,338) and does not contact the member that is formed with the groove (38,138,238,338), to a sealing position, at which position the secondary oil seal does not oppose the groove (38,138,238,338) and contacts the member that is formed with the groove (38,138,238,338), and the dust seal (22,242,342) is coupled to one of the first member and the second member and contacts another of the first member and the second member without opposing the groove both when the secondary oil seal is positioned at the reserve position and when the secondary oil seal is positioned at the sealing position.