Seat cushion

1. A seat cushion having a cushion length variable mechanism configured to adjust a length of a seating surface in a front-rear direction, the seat cushion comprising:

a cushion rear portion forming a rear portion of the seating surface;

a cushion front portion forming a front portion of the seating surface and being configured to approach and separate from the cushion rear portion in a front-rear direction by the cushion length variable mechanism;

a cushion cover covering the cushion front portion and the cushion rear portion;

a retraction member disposed over a cover back surface of the cushion cover to a first member among the cushion front portion and the cushion rear portion; and

a push-in member provided on a second member among the cushion front portion and the cushion rear portion, and configured to push the retraction member by the cushion front portion approaching the cushion rear portion, thereby retracting the cushion cover into a gap between the cushion front portion and the cushion rear portion with the retraction member.

2. The seat cushion according to claim 1 , wherein

the retraction member is attached to the first member by being attached to a first frame forming a frame of the first member.

3. The seat cushion according to claim 1 , wherein

the push-in member includes a frame member fixed to a second frame forming a frame of the second member.

4. The seat cushion according to claim 1 , wherein

the retraction member is configured to apply tension to retract the cushion cover into the gap even at a maximum separation position at which the cushion front portion is separated most from the cushion rear portion.

5. The seat cushion according to claim 4 , wherein

the cushion cover includes a rear cover, a front cover, and a seam allowance portion for sewing the rear cover and the front cover together,

the rear cover is configured to apply a first tension for pulling the seam allowance portion in a first direction,

the front cover is configured to apply a second tension for pulling the seam allowance portion in a second direction different from the first direction, and

the retraction member is configured to apply a third tension for polling the seam allowance portion in a third direction different from the first direction and the second direction.

6. The seat cushion according to claim 1 , wherein

the retraction member includes a flexible portion configured to be bent by being pressed by the push-in member.

7. A seat cushion having a cushion length variable mechanism configured to adjust a length of a seating surface in a front-rear direction, the seat cushion comprising:

a cushion rear portion forming a rear portion of the seating surface;

a cushion front portion forming a front portion of the seating surface and being configured to approach and separate from the cushion rear portion in a front-rear direction by the cushion length variable mechanism;

a cushion cover covering the cushion front portion and the cushion rear portion;

a retraction member disposed over a cover back surface of the cushion cover to a first member among the cushion front portion and the cushion rear portion; and

a push-in member provided on a second member among the cushion front portion and the cushion rear portion, and configured to push the retraction member by the cushion front portion approaching the cushion rear portion, thereby retracting the cushion cover into a gap between the cushion front portion and the cushion rear portion with the retraction member, wherein

the retraction member includes a first retraction portion sewn in a shape continuously extending in the seat width direction along the cover back surface, a wire passed through a tubular portion extending in a tubular shape in the seat width direction formed in the first retraction portion, and a second retraction portion bridged between a part of the wire in the seat width direction and the first member, and the push-in member is configured to be pressed against the second retraction portion.