To suppress the heightening of a seating level even when a leg placement part having wall parts is placed on a seat base.

The seat includes: a leg placement part 4 having a leg placement surface 41a to place the legs of a user and wall parts 42 erected from the leg placement surface 41a; and a seat base part 2 on which the leg placement part 4 is placed with the leg placement surface 41a directed downward. The leg placement part 4 and the seat base part 2 are changeable between a first state where the leg placement part 4 is placed on the seat base part 2 with the leg placement surface 41a directed downward and a second state where the leg placement part 4 is positioned in front of the seat base part 2 with the leg placement surface 41a directed upward. In the seat base part 2, the erecting direction top end part 42b of each wall part is permitted to be positioned lower than the upper surface 23a of the seat base part 2 in the first state.