A suspension device comprising a dust cover that is formed of a thermoplastic resin molded by blow molding, that is configured to cover an outer side of a damper extending in a predetermined direction, and that is substantially cylindrical, the dust cover comprising: - bellows portions that are formed in a predetermined section in an axial direction in the dust cover, that are inclined alternately toward a radially outer side and a radially inner side in the axial direction, that each has a radially outer end thinner than a radially inner end, and that are configured to expand and contract in the axial direction; - a flange portion that is formed at a predetermined position in the axial direction of the dust cover and extends radially outward from a cylindrical portion of the dust cover; and - a protrusion that forms one end of the dust cover in the axial direction and protrudes from the flange portion to one side in the axial direction, wherein the flange portion protrudes radially outward from the cylindrical portion of the dust cover by a dimension larger than a height dimension in a radial direction between the radially inner end and the radially outer end of each of the bellows portions, wherein a thickness of the flange portion is larger than a thickness of the radially outer end of each of the bellows portions, wherein the flange portion is disposed at one end side of the dust cover in the axial direction, and wherein the dust cover is disposed such that the axial direction is an up and down direction, the suspension device further comprising: - the damper whose radially outer side is covered by the dust cover; - a coil spring disposed at a radially outer side of the dust cover; - a mount portion to which an upper end side of the damper is connected and that is attached to a vehicle body; and - an upper seat that is disposed at a lower side of the mount portion and receives an upper end of the coil spring, wherein the flange portion of the dust cover is interposed between the mount portion and the upper seat, and wherein the mount portion includes a recessed portion that is formed on a lower surface of the mount portion and receives the protrusion of the dust cover. - bellows portions that are formed in a predetermined section in an axial direction in the dust cover, that are inclined alternately toward a radially outer side and a radially inner side in the axial direction, that each has a radially outer end thinner than a radially inner end, and that are configured to expand and contract in the axial direction; - a flange portion that is formed at a predetermined position in the axial direction of the dust cover and extends radially outward from a cylindrical portion of the dust cover; and - a protrusion that forms one end of the dust cover in the axial direction and protrudes from the flange portion to one side in the axial direction, wherein the flange portion protrudes radially outward from the cylindrical portion of the dust cover by a dimension larger than a height dimension in a radial direction between the radially inner end and the radially outer end of each of the bellows portions, wherein a thickness of the flange portion is larger than a thickness of the radially outer end of each of the bellows portions, wherein the flange portion is disposed at one end side of the dust cover in the axial direction, and wherein the dust cover is disposed such that the axial direction is an up and down direction, the suspension device further comprising: - the damper whose radially outer side is covered by the dust cover; - a coil spring disposed at a radially outer side of the dust cover; - a mount portion to which an upper end side of the damper is connected and that is attached to a vehicle body; and - an upper seat that is disposed at a lower side of the mount portion and receives an upper end of the coil spring, - the damper whose radially outer side is covered by the dust cover; - a coil spring disposed at a radially outer side of the dust cover; - a mount portion to which an upper end side of the damper is connected and that is attached to a vehicle body; and - an upper seat that is disposed at a lower side of the mount portion and receives an upper end of the coil spring, wherein the flange portion of the dust cover is interposed between the mount portion and the upper seat, and wherein the mount portion includes a recessed portion that is formed on a lower surface of the mount portion and receives the protrusion of the dust cover.