A seat structure has a main body and a seating surface element attached to the main body extending in a longitudinal direction. A back element is connected to a rear end of the seating surface element and is reclinable and extends in a vertical direction. The back element includes a back plate and a pair of back rods respectively positioned on both lateral sides of said back plate. An upper end flap is connected to an upper end of the back plate in a forward tiltable manner. A displacement member is supported on the back rods and is vertically displaceable. A first connection element connects the displacement member and upper end flap to tilt the upper end flap forward according to displacement of the displacement member.