A walking assistance device has a drive mechanism, which is provided with a linear-motion actuator including an electric motor installed in the upper link member, nut members which are rotationally driven by the electric motor, and a linear-motion output shaft which linearly moves in the direction of the axial centers of the nut members, and a crank arm which is secured to the lower link member coaxially with a joint axis of a third joint and swingably attached to one end of the linear-motion output shaft. The drive mechanism is constructed such that a translational force output from the linear-motion output shaft of the linear-motion actuator is converted into a rotational driving force of the third joint through the crank arm.