An actuator is reduced in weight without impairing a walking assist function, and this reduces the inertial moment of a leg link. A drive crank arm on the output shaft of the actuator and a driven crank arm fixed to a second link portion so as to be concentric to the joint shaft of a third joint portion are connected to each other via a connection link. The connection link is placed so that a line connecting a pivot portion at which the drive crank arm is pivotally mounted and a pivot portion at which the driven crank arm is pivotally mounted obliquely crosses a line connecting the output shaft of the actuator and the joint shaft of the third joint portion.