A seat apparatus includes a seat adapted to be arranged on a floor of a vehicle, a motor driving the seat to move, and a control unit supplying electric power to the motor by controlling a duty ratio with duty cycle control. The control unit determines an initial start-up time in which the duty ratio is defined as a first duty ratio over a period between the time the motor is started up after being powered by the control unit and the time before the seat driven by the motor starts moving. The control unit reduces the duty ratio when the initial start-up time elapses and sets the duty ratio to a second duty ratio smaller than the first duty ratio when the seat starts moving.