To provide a seat adjustment device capable of flexibly changing a shape of a seat. A seat adjustment device for adjusting a shape of a seat includes a pad including an elastomer, and airbags disposed on a front surface and a rear surface of the pad. The airbags are adjustable in amount of air therein. The airbags include a first airbag disposed on one of the front and rear surfaces and of the pad, and a second airbag disposed on the other. The first airbag is longer than the second airbag in a direction substantially perpendicular to the front and rear surfaces of the pad. The second airbag is longer than the first airbag in a direction substantially parallel to the front and rear surfaces of the pad.