A multi-resonant antenna comprising a main antenna and an additional radiation element, wherein: the main antenna comprises a main portion, which forms a split ring resonator, and a feeding portion, which branches off from the main portion; and the additional radiation element extends outward of the main antenna from the main antenna, wherein: the multi-resonant antenna comprises a substrate with a conductive pattern; the main portion of the main antenna is formed of a combination of at least one part of the conductive pattern on the substrate and a metal member which is distinct and separated from the substrate; the multi-resonant antenna comprises a ground portion; the additional radiation element does not overlap with the ground portion in a plan view, wherein the plan view is a view of the multi-resonant antenna from a direction perpendicular to a plane where the main antenna and the additional radiation element are arranged; the additional radiation element has a first extension portion extending in a first predetermined direction (negative X-direction); and the ground portion has a second extension portion which is apart from the first extension portion in a second predetermined direction (positive Y-direction) perpendicular to the first predetermined direction and which extends in the first predetermined direction, wherein: the ground portion has a third extension portion extending from the second extension portion in the second predetermined direction; and the first extension portion of the additional radiation element has a tip which is apart from and faces the third extension portion in the first predetermined direction. the main antenna comprises a main portion, which forms a split ring resonator, and a feeding portion, which branches off from the main portion; and the additional radiation element extends outward of the main antenna from the main antenna, wherein: the multi-resonant antenna comprises a substrate with a conductive pattern; the main portion of the main antenna is formed of a combination of at least one part of the conductive pattern on the substrate and a metal member which is distinct and separated from the substrate; the multi-resonant antenna comprises a ground portion; the additional radiation element does not overlap with the ground portion in a plan view, wherein the plan view is a view of the multi-resonant antenna from a direction perpendicular to a plane where the main antenna and the additional radiation element are arranged; the additional radiation element has a first extension portion extending in a first predetermined direction (negative X-direction); and the ground portion has a second extension portion which is apart from the first extension portion in a second predetermined direction (positive Y-direction) perpendicular to the first predetermined direction and which extends in the first predetermined direction, wherein: the ground portion has a third extension portion extending from the second extension portion in the second predetermined direction; and the first extension portion of the additional radiation element has a tip which is apart from and faces the third extension portion in the first predetermined direction. the multi-resonant antenna comprises a substrate with a conductive pattern; the main portion of the main antenna is formed of a combination of at least one part of the conductive pattern on the substrate and a metal member which is distinct and separated from the substrate; the multi-resonant antenna comprises a ground portion; the additional radiation element does not overlap with the ground portion in a plan view, wherein the plan view is a view of the multi-resonant antenna from a direction perpendicular to a plane where the main antenna and the additional radiation element are arranged; the additional radiation element has a first extension portion extending in a first predetermined direction (negative X-direction); and the ground portion has a second extension portion which is apart from the first extension portion in a second predetermined direction (positive Y-direction) perpendicular to the first predetermined direction and which extends in the first predetermined direction, wherein: the ground portion has a third extension portion extending from the second extension portion in the second predetermined direction; and the first extension portion of the additional radiation element has a tip which is apart from and faces the third extension portion in the first predetermined direction. the ground portion has a third extension portion extending from the second extension portion in the second predetermined direction; and the first extension portion of the additional radiation element has a tip which is apart from and faces the third extension portion in the first predetermined direction.