PURPOSE: To automatically reproduce the seat surface characteristic by providing a storage means for coordinating and storing the elapsed time from the start of seating, and a control means for controlling a driving means so as to reproduce the seat surface characteristic varied in accordance with the elapsed time.

CONSTITUTION: When a manual mode is selected by a mode selecting switch 21, whether volumes H1-H7 are operated or not is decided successively. When one volume Hn is operated, a driving signal is outputted to a motor 15 and a pressure reducing pump 12 is operated, an output of the operated volume concerned Hn and a sensor output of the pressure sensor concerned Pn corresponding thereto are read in, and a changeover valve Vn of the corresponding divided cushion Cn is controlled. In such a way, in the case the manual mode is set, by operating the volumes H1-H7 in order, internal pressure of the divided cushions C1-C7 is adjusted in order, and a seat surface characteristic of a front seat 1 can be adjusted to a characteristic being comfortable to sit on.