We propose a method to visualize a subspace in which a person or an object could exist. The subspace is defined by perspective projection property of an environmental camera. The shape of the subspace forms a cone and it is called object cone. Because the object cone is far from the original shape of the object, it is difficult to recognize its shape and range in a scene. We propose to place multiple vertical cross sections in the object cone. This visualization method is named multiple slits. This paper defines the formulation of the multiple slits, and we discuss expected effect on people perception of the object cone.