To effectively reduce the fatigue of a sitting person caused by elements which are internal pressure rise of the intervertebral disk due to an attitude in a seat for an automobile, tonus of the skeletal muscles, loads on the skin and skeletal muscles due to local pressurization and sitting time.

Air bags 3a, 3b, 4a and 4b for adjusting the supporting pressure of the sitting person by controlling seat surface hardness are built in the tuber ischiadicum support part 1 of a seat cushion 1 and the sacrum/ilium support part 2a and ninth thoracic vertebra support part 2b of a seat back 2 and is also built in the femoral lower part support part 1b of the seat cushion 1 as needed.