An antenna, comprising, in at least part of a radiation plate: a first surface formed so as to be oblique with respect to a second surface; and the second surface connected to the first surface so as to form an obtuse angle with respect to the first surface, wherein a connection portion between the first surface and the second surface has a smaller width than the first surface; the first surface comprises a slit that extends into the first surface from an edge of the first surface, the edge being parallel to the second surface and located adjacent to the connection portion; when viewing the first surface perpendicularly from above such that the edge is located at the top, the slit extends in a first segment downwards perpendicularly to the edge, then in a second segment to the right perpendicularly to the first segment, then in a third segment downwards perpendicularly to the second segment, then in a fourth segment to the left perpendicularly to the third segment, and then in a fifth segment upwards perpendicularly to the fourth segment; the slit ends with the fifth segment of the slit; the second segment of the slit is shorter than the fourth segment of the slit; the third segment of the slit is shorter than the fifth segment of the slit; the end of the fifth segment of the slit is located within the first surface; a first connecting point is located on the first surface in a region between the second segment, the third segment, and the fourth segment of the slit on the left side of the third segment of the slit; a second connecting point is located on the first surface on the right side of the third segment opposite to the first connecting point; the antenna is adapted to be fed with power through a coaxial cable; the first connecting point is fixed to an inner conductor of the coaxial cable; and the second connecting point is fixed to an outer conductor of the coaxial cable. a first surface formed so as to be oblique with respect to a second surface; and the second surface connected to the first surface so as to form an obtuse angle with respect to the first surface, wherein a connection portion between the first surface and the second surface has a smaller width than the first surface; the first surface comprises a slit that extends into the first surface from an edge of the first surface, the edge being parallel to the second surface and located adjacent to the connection portion; when viewing the first surface perpendicularly from above such that the edge is located at the top, the slit extends in a first segment downwards perpendicularly to the edge, then in a second segment to the right perpendicularly to the first segment, then in a third segment downwards perpendicularly to the second segment, then in a fourth segment to the left perpendicularly to the third segment, and then in a fifth segment upwards perpendicularly to the fourth segment; the slit ends with the fifth segment of the slit; the second segment of the slit is shorter than the fourth segment of the slit; the third segment of the slit is shorter than the fifth segment of the slit; the end of the fifth segment of the slit is located within the first surface; a first connecting point is located on the first surface in a region between the second segment, the third segment, and the fourth segment of the slit on the left side of the third segment of the slit; a second connecting point is located on the first surface on the right side of the third segment opposite to the first connecting point; the antenna is adapted to be fed with power through a coaxial cable; the first connecting point is fixed to an inner conductor of the coaxial cable; and the second connecting point is fixed to an outer conductor of the coaxial cable.