To obtain an apparatus with a simple structure and an accurate operation by a complete passive system by supporting a spreading body in the vertical direction from a fastened support position even when a moving object causes an oscillation incurring a pendulum motion with the fastened support position as fulcrum.

A vertical force is applied to an upper rotary connector D1 working on the weight of a stretcher to hold a balance support shaft B horizontally and a pointer I vertically. When an oscillatory body A is inclined under no lateral acceleration, gravity by a weight W and a moving object G vertically works on a distance holding body H linked to a balance holder P2 and when a friction force is small between a fastened support shaft O and the balance holders P1 and P2, no change occurs in attitude. When lateral acceleration is applied, no change occurs in the attitude about the center of the balance holder P1 and the moving object G having the weight W mounted thereon shifts its position in the direction O of a combined force of the gravity and the lateral acceleration on a circumference with a fixed distance from the center O and the stretcher is pulled by a lower rotary connector D2 to be stretched. But a spreading body C will not change in attitude and can be held stable.