To provide an device for assisting exercise which urges a seated user to perform exercise equivalent to walking exercise and thereby to improve the muscular strength of the right and left legs, by moving a seat portion of a chair taken by the user in the right and left directions alternately so as to shift the center of gravity of the body of the user.

When a driving portion 30 operates, the seat portion 21 is tilted in the right and left directions with the operation of the driving portion 30. When the seat portion 21 is tilted in the right and left directions, a left-end distance between the left end 21A1 of the seating surface of the seat portion 21 and a floor surface and a right-end distance between the right end 21A2 of the seating surface and the floor surface change. By the changes of the left-end distance and the right-end distance, a balance of the center of gravity of the user seated in the seat portion 21 is made unstable. On the occasion, the user presses down on a left side step portion 52A and a right side step portion 52B of a footstool 5 by the heels so as to correct the balance of the center of gravity which is made unstable when the seat portion 21 is tilted. With repetition of tilting of the seat portion 21, the user repeats pressing-down motion by the right and left heels and thus performs the exercise equivalent to the walking exercise.