A seat apparatus to be mounted on a vehicle, comprising: a seat cushion frame; a seat back frame which is arranged so as to stand from a back end part of the seat cushion frame; a cornering sensor which detects a cornering direction of the vehicle; and a control unit which controls the seat back frame on a basis of a detection result obtained by the cornering sensor, wherein the seat back frame includes: left and right side frames (51, 52) which are respectively arranged at two side parts of the seat back frame so as to extend in a vertical direction; and an adjustment mechanism which engages with the left and right side frames (51,52) and which adjusts a posture of a driver, wherein the control unit controls the adjustment mechanism to adjust the posture of the driver on the basis of the detection result obtained by the cornering sensor, wherein the adjustment mechanism comprises: a backboard which is arranged between the left and right side frames; and a swing mechanism which swings the backboard with respect to a traveling direction of the vehicle, wherein the control unit adjusts the posture of the driver by controlling the swing mechanism to swing the backboard, and wherein the swing mechanism includes: a first connection unit which connects one of the left and right side frames (51,52) and one side part of the backboard; a first drive source which swings the one side part of the backboard in the front-back direction by moving the first connection unit; a second connection unit which connects the other of the left and right side frames and the other side part of the backboard; and a second drive source which swings the other side part of the backboard by moving the second connection unit, and wherein the control unit controls the swing mechanism by controlling at least one of the first drive source and the second drive source. a seat cushion frame; a seat back frame which is arranged so as to stand from a back end part of the seat cushion frame; a cornering sensor which detects a cornering direction of the vehicle; and a control unit which controls the seat back frame on a basis of a detection result obtained by the cornering sensor, wherein the seat back frame includes: left and right side frames (51, 52) which are respectively arranged at two side parts of the seat back frame so as to extend in a vertical direction; and an adjustment mechanism which engages with the left and right side frames (51,52) and which adjusts a posture of a driver, left and right side frames (51, 52) which are respectively arranged at two side parts of the seat back frame so as to extend in a vertical direction; and an adjustment mechanism which engages with the left and right side frames (51,52) and which adjusts a posture of a driver, wherein the control unit controls the adjustment mechanism to adjust the posture of the driver on the basis of the detection result obtained by the cornering sensor, wherein the adjustment mechanism comprises: a backboard which is arranged between the left and right side frames; and a swing mechanism which swings the backboard with respect to a traveling direction of the vehicle, wherein the control unit adjusts the posture of the driver by controlling the swing mechanism to swing the backboard, and a backboard which is arranged between the left and right side frames; and a swing mechanism which swings the backboard with respect to a traveling direction of the vehicle, wherein the control unit adjusts the posture of the driver by controlling the swing mechanism to swing the backboard, and wherein the swing mechanism includes: a first connection unit which connects one of the left and right side frames (51,52) and one side part of the backboard; a first drive source which swings the one side part of the backboard in the front-back direction by moving the first connection unit; a second connection unit which connects the other of the left and right side frames and the other side part of the backboard; and a second drive source which swings the other side part of the backboard by moving the second connection unit, and wherein the control unit controls the swing mechanism by controlling at least one of the first drive source and the second drive source. a first connection unit which connects one of the left and right side frames (51,52) and one side part of the backboard; a first drive source which swings the one side part of the backboard in the front-back direction by moving the first connection unit; a second connection unit which connects the other of the left and right side frames and the other side part of the backboard; and a second drive source which swings the other side part of the backboard by moving the second connection unit, and wherein the control unit controls the swing mechanism by controlling at least one of the first drive source and the second drive source.