To provide a simple rotary seat for vehicle which simplifies a conversion mechanism of seat arrangement, reduces the manufacturing cost, and facilitates conversion operation.

A rotary shaft 6 of a vehicular seat 2 is offset from the center of the seat 2, a clearance is provided on a rear side of a backrest of the seat 2, and a corner part 9 on a rear surface of a backrest part 4 of the seat 2 is cut to prevent the contact of the seat 2 with a side wall 1 of a vehicle at the time of rotation so as to provide the combined use type seat 2 which can convert the arrangement of the seat 2 by a rotary mechanism only, reduces the manufacturing cost, and facilitates conversion operation.