An antenna device (1a, 1c) comprising: a first dielectric substrate, wherein a first surface is one surface of the first dielectric substrate, and a second surface is the other surface of the first dielectric substrate; a first ground provided on the first surface and having a strip shape; a plurality of first strip lines (7a-1 to 7d-1, 7a-2 to 7d-2) provided on the first surface; a plurality of holes (6a-6e, 10a-10d) provided in the first ground (4b, 4c); a signal line provided on the second surface facing opposite to the first surface, the signal line disposed at a position corresponding to the position of the first ground (4b, 4c), and wherein the signal line is configured such that high frequency wave propagates through the signal line; a plurality of branch lines (5a-5d) provided on the second surface and branched from the signal line; wherein the strip shape of the first ground (4b, 4c) is parallel to the signal line, each of the first strip lines (7a-1 to 7d-1, 7a-2 to 7d-2) is a strip line extending from the first ground (4b, 4c), each of the holes (6a-6e, 10a-10d) intersects with a straight line along a corresponding one of the first strip lines (7a-1 to 7d-1, 7a-2 to 7d-2), and a projection of each of the branch lines (5a-5d) on the first surface intersects with a corresponding one of the holes (6a-6e, 10a-10d) located on the first surface; characterized in that the length of the first ground in the longitudinal direction is equal to the length from a first end of the dielectric substrate along the longitudinal direction of the first ground (4b, 4c) to the first strip line closest to a second end of the dielectric substrate and a hole of the plurality of holes (6a-6e, 10a-10d) that intersects with a straight line along the first strip line closest to the second end of the dielectric substrate is open on the second end side of the dielectric substrate. a first dielectric substrate, wherein a first surface is one surface of the first dielectric substrate, and a second surface is the other surface of the first dielectric substrate; a first ground provided on the first surface and having a strip shape; a plurality of first strip lines (7a-1 to 7d-1, 7a-2 to 7d-2) provided on the first surface; a plurality of holes (6a-6e, 10a-10d) provided in the first ground (4b, 4c); a signal line provided on the second surface facing opposite to the first surface, the signal line disposed at a position corresponding to the position of the first ground (4b, 4c), and wherein the signal line is configured such that high frequency wave propagates through the signal line; a plurality of branch lines (5a-5d) provided on the second surface and branched from the signal line; wherein the strip shape of the first ground (4b, 4c) is parallel to the signal line, each of the first strip lines (7a-1 to 7d-1, 7a-2 to 7d-2) is a strip line extending from the first ground (4b, 4c), each of the holes (6a-6e, 10a-10d) intersects with a straight line along a corresponding one of the first strip lines (7a-1 to 7d-1, 7a-2 to 7d-2), and a projection of each of the branch lines (5a-5d) on the first surface intersects with a corresponding one of the holes (6a-6e, 10a-10d) located on the first surface; characterized in that the length of the first ground in the longitudinal direction is equal to the length from a first end of the dielectric substrate along the longitudinal direction of the first ground (4b, 4c) to the first strip line closest to a second end of the dielectric substrate and a hole of the plurality of holes (6a-6e, 10a-10d) that intersects with a straight line along the first strip line closest to the second end of the dielectric substrate is open on the second end side of the dielectric substrate.