A walking assist device which assists walking motion of one of the legs of the human with a sensor attached only to the one leg is provided. The walking assist device comprises an actuator, a sensor, and a controller. The sensor detects a knee joint angle and a hip joint angle of the one leg. The controller stores a first target trajectory for the knee joint angle and a second target trajectory for the hip joint angle. The controller controls the actuator so that the detected knee joint angle follows the first target trajectory. Further, the controller compares time series data of the detected hip joint angle with the second target trajectory while the one leg is in a stance phase. The controller calculates a time difference between the time series data and the second target trajectory and modifies the first target trajectory based on the time difference.
