A vehicle seat apparatus includes a seat, an actuator, and a controller in which a posture control unit exercises a seat posture control over the actuator based on a lateral acceleration and a steering velocity, to change an orientation of at least a portion of the seat. The posture control unit is configured to activate the seat posture control when a magnitude of the lateral acceleration becomes greater than a first acceleration threshold value, as well as to activate the seat posture control on conditions that the steering velocity has a magnitude greater than a steering velocity threshold value and when the magnitude of the lateral acceleration becomes greater than a second acceleration threshold value of which a magnitude is smaller than the first acceleration threshold value and a direction is laterally opposite to a direction of the steering velocity.