To expand an application range of a Karman's vortex reducing body and to enhance a degree of freedom at an application portion by providing the reducing body freely attachable/detachable to/from a surface of an object in contact with fluid and made of a base material provided with many projecting parts, recessed parts, projecting lines or recessed grooves on a surface.

In this Karman's vortex reducing body 1, a synthetic resin sheet 10 is made as a base material, a semi-spherical synthetic resin projecting part 2 is molded integrally with the surface, and an adhesive layer 11 and a peeling sheet 12 are adhered to a rear face of the sheet 10. When the body 1 is used, the reducing body 1 is cut according to an adhering object portion, and the peeling sheet 12 is peeled and adhered to a surface of an automobile. At the time of a traveling, air turbulence flowing from an advancing direction collides against the projecting part 2 and is collapsed, regularity of turbulence is lost, each vortex itself is made small, a Karman's vortex is prevented from being formed, and wind noise and air resistance are reduced. By the constitution, a user himself can freely select a mounting portion and a range of the reducing body 1 and the projecting part 2, an application range is expanded and a degree of freedom of an application portion is enhanced.