A fixing device for a motion assistance apparatus comprising: a first side frame including: a first central portion configured to attach to one side of a user; a first front extending portion configured to extend from the first central portion along a front side of the user; and a first rear extending portion configured to extend from the first central portion along a rear side of the user; and a second side frame including: a second central portion configured to attach to another side of the user such that the second central portion faces the first central portion and is separated from the first central portion by a distance with a portion of user enclosed therebetween, the distance between the first central portion and the second central portion being adjustable; a second front extending portion configured to extend from the second central portion along the front side of the user; and a second rear extending portion configured to extend from the second central portion along the rear side of the user, wherein the first front extending portion and the second front extending portion are detachable from one another and configured to overlap around a front side of the user in a front overlapping area that is adjustable, wherein at least one of the first side frame and the second side frame further comprises: a supporting member (140, 240, 500, 620, 700) configured to extend from a rear extending portion of the at least one side frame in one or more of a cranial or caudal direction; characterised in that the first rear extending portion and the second rear extending portion are detachable from one another and configured to overlap around a rear side of the user in an rear overlapping area that is adjustable, wherein the first rear extending portion is configured to slide with respect to the second rear extending portion. a first side frame including: a first central portion configured to attach to one side of a user; a first front extending portion configured to extend from the first central portion along a front side of the user; and a first rear extending portion configured to extend from the first central portion along a rear side of the user; and a first central portion configured to attach to one side of a user; a first front extending portion configured to extend from the first central portion along a front side of the user; and a first rear extending portion configured to extend from the first central portion along a rear side of the user; and a second side frame including: a second central portion configured to attach to another side of the user such that the second central portion faces the first central portion and is separated from the first central portion by a distance with a portion of user enclosed therebetween, the distance between the first central portion and the second central portion being adjustable; a second front extending portion configured to extend from the second central portion along the front side of the user; and a second rear extending portion configured to extend from the second central portion along the rear side of the user, wherein the first front extending portion and the second front extending portion are detachable from one another and configured to overlap around a front side of the user in a front overlapping area that is adjustable, a second central portion configured to attach to another side of the user such that the second central portion faces the first central portion and is separated from the first central portion by a distance with a portion of user enclosed therebetween, the distance between the first central portion and the second central portion being adjustable; a second front extending portion configured to extend from the second central portion along the front side of the user; and a second rear extending portion configured to extend from the second central portion along the rear side of the user, wherein the first front extending portion and the second front extending portion are detachable from one another and configured to overlap around a front side of the user in a front overlapping area that is adjustable, wherein at least one of the first side frame and the second side frame further comprises: a supporting member (140, 240, 500, 620, 700) configured to extend from a rear extending portion of the at least one side frame in one or more of a cranial or caudal direction; characterised in that the first rear extending portion and the second rear extending portion are detachable from one another and configured to overlap around a rear side of the user in an rear overlapping area that is adjustable, wherein the first rear extending portion is configured to slide with respect to the second rear extending portion. a supporting member (140, 240, 500, 620, 700) configured to extend from a rear extending portion of the at least one side frame in one or more of a cranial or caudal direction; characterised in that the first rear extending portion and the second rear extending portion are detachable from one another and configured to overlap around a rear side of the user in an rear overlapping area that is adjustable, wherein the first rear extending portion is configured to slide with respect to the second rear extending portion.