A walking assistance device and method for providing an assist torque to an ankle of a user is provided. To provide an assist torque to an ankle of a user, the walking assistance device generates a leg image by capturing a second leg using a camera attached to a first leg, determines a gait state of the second leg based on the leg image, determines an assist torque value output to the first leg based on the gait state of the second leg, and controls a driving device such that the assist torque value is output to the first leg.