Abstract: Operation force required for pivot operation of a movable body can be set almost constant independent of variation in the angular position of the pivoting. A pivot mechanism (tumble mechanism (10A)) has a floor-side member (B) fixed to a predetermined position; a seat-side member (12) connected to the floor side member (B) by hinge coupling so as to be pivotable in a predetermined angle range; and a torsion spring member (14)provided to urge the seat side member (12)in the opposite direction to gravity that acts on the seat side member (12). The pivot mechanism is constructed such that weight moments about a pivot center (13a) acting on the seat-side member (12) as the pivot mechanism move varies. The torsion spring member (14) has an urging the section (14b) for urging the seat seat member (12) and a support section (14a) that is supported by the floor side member (B).

Abstract: It is intended that an operation force required for pivoting a movable body can be maintained substantially constant regardless of an angular position of pivot of the movable body. A pivot mechanism (a tumble mechanism 10A) includes a floor-side member B fixed to a desired position, a seat-side member 12 coupled to the floor-side member B by hinge coupling so as to be pivotable within a predetermined angle range, and a torsion spring member 14 arranged to bias the seat-side member 12 in a pivot direction opposite to the gravitational force acting on the seat-side member 12. The pivot mechanism is constructed such that gravitational moments about a pivot center 13a acting on the seat-side member 12 can be changed depending on pivoting thereof. The torsion spring member 14 has an biasing section 14b for biasing the seat-side member 12 and a support section 14a supported on the floor-side member B.