An ankle joint mechanism to be fitted on an ankle of a user to assist motion of a body of the user, includes: a lower leg link to be disposed along a lower leg of the user a foot holder configured to hold a foot of the user a plantar/dorsi flexion mechanism configured to connect the lower leg link and the foot holder to each other so as to be pivotable about a plantar/dorsi flexion axis of an ankle joint of the user an adduction/abduction mechanism configured to connect the lower leg link and the foot holder to each other so as to be pivotable about an adduction/abduction axis of the ankle joint and an inversion/eversion mechanism configured to connect the lower leg link and the foot holder to each other so as to be pivotable about an inversion/eversion axis of the ankle joint.
