Disclosed is an operation assisting device which is excellent in portability and can be easily configured in a wearable manner. An air bag that is disposed along a direction orthogonal to the pivot axis of the joint so as to cover the body surface around the joint and is substantially rectangular in a front view that is long in the direction perpendicular to the pivot axis. A holding portion that holds the peripheral portion of the air bag and has flexibility, and one end side of the air bag on the back side with respect to the body surface on which the air bag is mounted, in a direction perpendicular to the swing axis than the air bag. A pair of belt bands fixed to the outer side of the side or the other side, the other end side being connected to the edge of one side or the other side of the holding portion, an air supply device for supplying air into the air bag, and an air An air exhaust device that exhausts the air supplied into the bag to the outside, and when the air bag is expanded when the air bag is expanded, the joint is connected via the holding portion and the pair of belt bands. When an acting force in the direction of extending the air is generated and the air in the air bag is exhausted and the air bag contracts Is, the acting force is lost. [Selection] Figure 1【課題】携帯性に優れ、容易にウェアラブルな構成にできる動作補助装置を提供する。【解決手段】関節の周囲の体表面を覆うように関節の揺動軸に対して直交する方向に沿って配置されて、揺動軸に直交する方向に長い正面視略矩形状のエア袋と、エア袋の周縁部を保持すると共に可撓性を有する保持部と、一端側が、エア袋が装着される体表面に対して背面側において、エア袋よりも揺動軸に直交する方向の一方側又は他方側の外側に固定され、他端側が、保持部の一方側又は他方側の端縁部に接続される一対のベルト帯と、エア袋内に空気を供給するエア供給装置と、エア袋内に供給された空気を外部に排気するエア排気装置と、を備え、エア袋内に空気が供給されて該エア袋が拡張した際には、保持部及び一対のベルト帯を介して関節を伸ばす方向の作用力が発生し、エア袋内の空気が排気されて該エア袋が収縮した際には、作用力が消失する。【選択図】図1