Seat device for vehicle

A seat device for a vehicle, comprising:

• a row of seats including two seats that are disposed separately in a width direction of the vehicle and include each seat cushion and seat back, the seat cushion of at least one of the seats comprising a cushion body portion that includes a storage recess with an upward opening and a cushion bottom portion that covers the opening of the storage recess so as to selectively open or close the opening;
• a supplementary seat disposed between said two seats and including a supplementary seat back and a supplementary seat cushion that are formed separately from each other, an upper end portion of the supplementary seat back being detachably supported on a side portion of the seat back of said one of the seats and a lower end portion thereof being pivotally supported on the side portion of the seat back of said one of the seats so as to allow the supplementary seat back to rotate in a longitudinal direction of the vehicle, the supplementary seat cushion disposed below the supplementary seat back and at a side of the seat cushion of said one of the seats;
• and
• a swing mechanism for pivoting said supplementary seat cushion of the supplementary seat so as to allow the supplementary seat cushion to swing substantially in the width direction of the vehicle, the swing mechanism allowing said supplementary seat cushion of the supplementary seat to selectively take a sitting position, where the supplementary seat cushion is located at the side of the seat cushion of said one of the seats, and a stored position, where the supplementary seat cushion is stored in the storage recess of the seat cushion body portion of said one of the seats.