A horizontal-component trap of atmospheric dustfall comprising: a dust sampling port that includes a ceiling plate, a side wall, and four or more partition plates; an air pipe; and a trap container that collects dustfall, flowing from the dust sampling port, through the air pipe, wherein the dust sampling port is connected to the air pipe, wherein the air pipe is connected to the trap container, wherein a lower end of the side wall is provided with an air port as an opening, wherein the air port is connected to the air pipe, wherein the side wall is provided with four or more external air inlets each having an opening disposed at the same interval in the circumferential direction of the side wall and disposed at a specific height near the upper end thereof, wherein the ceiling plate has a substantially disk shape, wherein the center axis of the ceiling plate is aligned with the center axis of the side wall, wherein the ceiling plate is connected to the upper end of the side wall so as to come into contact therewith, and wherein each of the four or more partition plates is a flat plate disposed in a vertical plane, characterized in that the side wall is a plate that has a vertical center axis and has a side surface having a shape of a substantially circular truncated cone or a polygonal truncated cone widened upward, each of the four or more partition plates is connected to the side wall and the ceiling plate without any gap formed therebetween, the four or more partition plates are connected to each other on the center axis of the ceiling plate, and the four or more partition plates divide a space surrounded by the side wall into fan-shaped areas having an equal size in a horizontal cross-section. a dust sampling port that includes a ceiling plate, a side wall, and four or more partition plates; an air pipe; and a trap container that collects dustfall, flowing from the dust sampling port, through the air pipe, wherein the dust sampling port is connected to the air pipe, wherein the air pipe is connected to the trap container, wherein a lower end of the side wall is provided with an air port as an opening, wherein the air port is connected to the air pipe, wherein the side wall is provided with four or more external air inlets each having an opening disposed at the same interval in the circumferential direction of the side wall and disposed at a specific height near the upper end thereof, wherein the ceiling plate has a substantially disk shape, wherein the center axis of the ceiling plate is aligned with the center axis of the side wall, wherein the ceiling plate is connected to the upper end of the side wall so as to come into contact therewith, and wherein each of the four or more partition plates is a flat plate disposed in a vertical plane, characterized in that the side wall is a plate that has a vertical center axis and has a side surface having a shape of a substantially circular truncated cone or a polygonal truncated cone widened upward, each of the four or more partition plates is connected to the side wall and the ceiling plate without any gap formed therebetween, the four or more partition plates are connected to each other on the center axis of the ceiling plate, and the four or more partition plates divide a space surrounded by the side wall into fan-shaped areas having an equal size in a horizontal cross-section.