An air suspension comprising: a cylinder including, on an upper end side thereof, a vehicle-body-side attachment member joined to a vehicle body; a piston rod including a piston on an upper end side thereof and inserted into the cylinder together with the piston; a cylindrical rod-side member disposed on a lower end side of the piston rod and opened at an upper end of the rod-side member and a lower end thereof; a diaphragm having an upper end of which is fixed to a side of the cylinder and a lower end of which is fixed to the rod-side member, the diaphragm forming an air chamber around the piston rod; an axle-side attachment member having an upper end side of which is fixed to the opening at the lower end of the rod-side member, the axle-side attachment member including, on an upper end face thereof, a fixing section fixing a lower end of the piston rod and, on a lower end side thereof, an attachment hole joined to an axle; a gas passage formed in the axle-side attachment member, one end of the gas passage being opened to the upper end face of the axle-side attachment member and the other end of the gas passage being opened to a side section of the axle-side attachment member; and a valve section provided at the opening of the other end of the gas passage, wherein the valve section includes: a valve main body that guides gas supplied from an outside to the gas passage; and a valve cap that seals the valve main body, the axle-side attachment member includes an annular groove around the gas passage on a side of the side section, and the valve cap is attached in a state where at least a part of the valve cap is inserted into the annular groove. a cylinder including, on an upper end side thereof, a vehicle-body-side attachment member joined to a vehicle body; a piston rod including a piston on an upper end side thereof and inserted into the cylinder together with the piston; a cylindrical rod-side member disposed on a lower end side of the piston rod and opened at an upper end of the rod-side member and a lower end thereof; a diaphragm having an upper end of which is fixed to a side of the cylinder and a lower end of which is fixed to the rod-side member, the diaphragm forming an air chamber around the piston rod; an axle-side attachment member having an upper end side of which is fixed to the opening at the lower end of the rod-side member, the axle-side attachment member including, on an upper end face thereof, a fixing section fixing a lower end of the piston rod and, on a lower end side thereof, an attachment hole joined to an axle; a gas passage formed in the axle-side attachment member, one end of the gas passage being opened to the upper end face of the axle-side attachment member and the other end of the gas passage being opened to a side section of the axle-side attachment member; and a valve section provided at the opening of the other end of the gas passage, wherein the valve section includes: a valve main body that guides gas supplied from an outside to the gas passage; and a valve cap that seals the valve main body, a valve main body that guides gas supplied from an outside to the gas passage; and a valve cap that seals the valve main body, the axle-side attachment member includes an annular groove around the gas passage on a side of the side section, and the valve cap is attached in a state where at least a part of the valve cap is inserted into the annular groove.