Airbags each belonging to one of first and second control blocks are arranged below the thighs of an occupant seated on a seat seating surface (S). Specifically, the first and second control blocks are arranged such that the airbags belonging thereto are adjacent to one another in the seat width direction. Further, a seat device controls the airbags belonging to the first control block and the airbags belonging to the second control block to alternately expand and contract.