A joint motion facilitation device, comprising: at least one bellows (211, 212, 213) provided for each joint in a predetermined subject body portion, and generating force to facilitate a joint motion, when provided to a joint portion in a direction perpendicular with respect to a rotational axis of rotation motion of said joint, and disposed on at least one of a flexion side and a extension side of the joint; wherein annular grooves are provided at regular intervals along an expansion and contraction direction upon said bellows; a conduit (130, 222, 223) that communicates with said bellows for providing air to said bellows at a regulated pressure to obtain an internal bellows pressure; an air pressure regulation part that is so configured as to regulate air pressure in the bellows via said conduit, and is suitable for performing supply of air to said bellows or exhaustion of air from said bellows; transmission members (231, 232, 233, 234) connected to end portions of said bellows, that, when mounted to said predetermined subject body portion, transmit force originating in expansion and contraction of said bellows to said joint for facilitating said joint motion; and mounting portions that mount said bellows and said transmission members to said predetermined subject body portion, characterized by further comprising a restraining member (241, 242, 243) of a elastic member that elastically restraints the annular grooves on the side of said bellows that faces said joint; said transmission members are made by bending metallic plates into L shape and/or U shape, said transmission members comprise an one-side-transmission-member suitable to be mounted to an one side body part of said predetermined subject body portion, said one side body part being connected to said joint, and an other-side-transmission-member suitable to be mounted to an other side body part of said predetermined subject body portion, said other side body part being connected to said joint, said restraining member is connected to both of a portion near said joint of said one-side-transmission-member and a portion near said joint of said other-side-transmission-member; said restraining member is suitable for adjusting the gaps of the annular grooves on the side of said bellows that faces said joint when the joint is in its flexed state or in its extended state; when exhausting of air from said bellows is performed, the internal bellows pressure attains a negative pressure, said restraining member converts force generated by the contraction of the bellows into a rotational force, and said rotational force is transmitted to said one side body part and said other side body part through said one-side-transmission-member and said other-side-transmission-member. at least one bellows (211, 212, 213) provided for each joint in a predetermined subject body portion, and generating force to facilitate a joint motion, when provided to a joint portion in a direction perpendicular with respect to a rotational axis of rotation motion of said joint, and disposed on at least one of a flexion side and a extension side of the joint; wherein annular grooves are provided at regular intervals along an expansion and contraction direction upon said bellows; a conduit (130, 222, 223) that communicates with said bellows for providing air to said bellows at a regulated pressure to obtain an internal bellows pressure; an air pressure regulation part that is so configured as to regulate air pressure in the bellows via said conduit, and is suitable for performing supply of air to said bellows or exhaustion of air from said bellows; transmission members (231, 232, 233, 234) connected to end portions of said bellows, that, when mounted to said predetermined subject body portion, transmit force originating in expansion and contraction of said bellows to said joint for facilitating said joint motion; and mounting portions that mount said bellows and said transmission members to said predetermined subject body portion, a restraining member (241, 242, 243) of a elastic member that elastically restraints the annular grooves on the side of said bellows that faces said joint; said transmission members are made by bending metallic plates into L shape and/or U shape, said transmission members comprise an one-side-transmission-member suitable to be mounted to an one side body part of said predetermined subject body portion, said one side body part being connected to said joint, and an other-side-transmission-member suitable to be mounted to an other side body part of said predetermined subject body portion, said other side body part being connected to said joint, said restraining member is connected to both of a portion near said joint of said one-side-transmission-member and a portion near said joint of said other-side-transmission-member; said restraining member is suitable for adjusting the gaps of the annular grooves on the side of said bellows that faces said joint when the joint is in its flexed state or in its extended state; when exhausting of air from said bellows is performed, the internal bellows pressure attains a negative pressure, said restraining member converts force generated by the contraction of the bellows into a rotational force, and said rotational force is transmitted to said one side body part and said other side body part through said one-side-transmission-member and said other-side-transmission-member.