A waveguide slot antenna comprising: a waveguide formed by a dielectric substrate, a first conductive layer formed at a lower surface of the dielectric substrate, a second conductive layer formed at an upper surface of the dielectric substrate, a pair of side wall parts (W1, W2) electrically connecting the first conductive layer and the second conductive layer and extending in a first direction that is a signal propagation direction in the waveguide; and a power feeding part formed so as to penetrate the dielectric substrate at least from the upper surface to the lower surface of the dielectric substrate such that the power feeding part penetrates the upper surface and the lower surface of the dielectric substrate, wherein the power feeding part is adapted to feed an input signal to the waveguide, wherein the input signal is configured to propagate in the propagation direction, wherein the second conductive layer is provided with one or a plurality of slots adapted to radiate electromagnetic waves derived from the input signal which is configured to propagate in the propagation direction, wherein the one or the plurality of slots includes a first slot having a predetermined slot length along the first direction, and wherein when viewed as a plan view from a second direction that is perpendicular to the second conductive layer, the power feeding part is arranged at a position where the power feeding part overlaps the first slot, and the power feeding part does not deviate from a range of the slot length along the first direction. a waveguide formed by a dielectric substrate, a first conductive layer formed at a lower surface of the dielectric substrate, a second conductive layer formed at an upper surface of the dielectric substrate, a pair of side wall parts (W1, W2) electrically connecting the first conductive layer and the second conductive layer and extending in a first direction that is a signal propagation direction in the waveguide; and a dielectric substrate, a first conductive layer formed at a lower surface of the dielectric substrate, a second conductive layer formed at an upper surface of the dielectric substrate, a pair of side wall parts (W1, W2) electrically connecting the first conductive layer and the second conductive layer and extending in a first direction that is a signal propagation direction in the waveguide; and a power feeding part formed so as to penetrate the dielectric substrate at least from the upper surface to the lower surface of the dielectric substrate such that the power feeding part penetrates the upper surface and the lower surface of the dielectric substrate, wherein the power feeding part is adapted to feed an input signal to the waveguide, wherein the input signal is configured to propagate in the propagation direction, wherein the second conductive layer is provided with one or a plurality of slots adapted to radiate electromagnetic waves derived from the input signal which is configured to propagate in the propagation direction, wherein the one or the plurality of slots includes a first slot having a predetermined slot length along the first direction, and wherein when viewed as a plan view from a second direction that is perpendicular to the second conductive layer, the power feeding part is arranged at a position where the power feeding part overlaps the first slot, and the power feeding part does not deviate from a range of the slot length along the first direction.