A seat has an erroneous operation preventing device for, locking movement of a seat strap to regulate the stowing or folding operation, the device including a movable member provided on a seat back side to be abutted with the strap, a first connecting member that is connectable to the movable member, a second connecting member connected to the first connecting member through a first connecting portion, a strap connecting member connected to the second connecting member through a second connecting portion and locked to one end portion side of the strap, and a regulator for regulating the movable member or the first connecting member movably toward one side, wherein the first connecting member is supported on a first movable shaft provided on the seat back side, and the first connecting portion is arranged to be moved to cross a straight line connecting the shaft portion and the second connecting portion.