A suspension for a vehicle comprising: an upper arm that has a tip end section that is connected by way of an upper joint to the upper portion of a knuckle by which a wheel is supported so as to be able to rotate, and a base end section that is supported by the vehicle so as to be able to pivot in the up-down direction; and a lower arm that has a tip end section that is connected by way of a lower joint to the lower portion of the knuckle, and a base end section that is supported by the vehicle so as to be able to pivot in the up-down direction; wherein the upper arm comprises: a casing that is supported by the vehicle so as to be able to pivot in the up-down direction; a pair of screw shafts that are located on the same axis in the forward-backward direction of the vehicle, and are supported by the casing so as to be able to move only in the axial direction; a pair of screw nuts that engage around the pair of screw shafts, and are supported by the casing so as only to be able to rotate; a worm wheel that is combined with the pair of screw nuts so as to be able to rotate in synchronization with the screw nuts; a worm that comprises worm teeth that engage with the worm wheel; an electric motor that is supported by the casing, and is able to rotate and drive the worm in both directions; and a pair of link arms that have a tip end section and a base end section, where the base end sections respectively connect to the tip end sections of the pair of screw shafts so as to be able to rotate around a shaft in the up-down direction of the vehicle, and the tip end sections respectively connect to the upper joints so as to be able to rotate around a shaft in the up-down direction of the vehicle, and wherein by the electric motor rotating and driving the worm so as to cause the pair of screw shafts to move out in opposite directions from each other in the axial direction, the opening angle of the pair of link arms changes, and thus the length of the pair of link arms in the width direction of the vehicle changes. an upper arm that has a tip end section that is connected by way of an upper joint to the upper portion of a knuckle by which a wheel is supported so as to be able to rotate, and a base end section that is supported by the vehicle so as to be able to pivot in the up-down direction; and a lower arm that has a tip end section that is connected by way of a lower joint to the lower portion of the knuckle, and a base end section that is supported by the vehicle so as to be able to pivot in the up-down direction; wherein the upper arm comprises: a casing that is supported by the vehicle so as to be able to pivot in the up-down direction; a pair of screw shafts that are located on the same axis in the forward-backward direction of the vehicle, and are supported by the casing so as to be able to move only in the axial direction; a pair of screw nuts that engage around the pair of screw shafts, and are supported by the casing so as only to be able to rotate; a worm wheel that is combined with the pair of screw nuts so as to be able to rotate in synchronization with the screw nuts; a worm that comprises worm teeth that engage with the worm wheel; an electric motor that is supported by the casing, and is able to rotate and drive the worm in both directions; and a pair of link arms that have a tip end section and a base end section, where the base end sections respectively connect to the tip end sections of the pair of screw shafts so as to be able to rotate around a shaft in the up-down direction of the vehicle, and the tip end sections respectively connect to the upper joints so as to be able to rotate around a shaft in the up-down direction of the vehicle, and wherein by the electric motor rotating and driving the worm so as to cause the pair of screw shafts to move out in opposite directions from each other in the axial direction, the opening angle of the pair of link arms changes, and thus the length of the pair of link arms in the width direction of the vehicle changes. a casing that is supported by the vehicle so as to be able to pivot in the up-down direction; a pair of screw shafts that are located on the same axis in the forward-backward direction of the vehicle, and are supported by the casing so as to be able to move only in the axial direction; a pair of screw nuts that engage around the pair of screw shafts, and are supported by the casing so as only to be able to rotate; a worm wheel that is combined with the pair of screw nuts so as to be able to rotate in synchronization with the screw nuts; a worm that comprises worm teeth that engage with the worm wheel; an electric motor that is supported by the casing, and is able to rotate and drive the worm in both directions; and a pair of link arms that have a tip end section and a base end section, where the base end sections respectively connect to the tip end sections of the pair of screw shafts so as to be able to rotate around a shaft in the up-down direction of the vehicle, and the tip end sections respectively connect to the upper joints so as to be able to rotate around a shaft in the up-down direction of the vehicle, and wherein by the electric motor rotating and driving the worm so as to cause the pair of screw shafts to move out in opposite directions from each other in the axial direction, the opening angle of the pair of link arms changes, and thus the length of the pair of link arms in the width direction of the vehicle changes.