A dielectric leaky wave antenna comprising: a dielectric substrate; a ground conductor provided on one surface side of the dielectric substrate, the ground conductor forming a dielectric image guide which propagates electromagnetic radiation in a direction perpendicular to a thickness direction in the dielectric substrate; and a plurality of metal strips for leakage (23, 23') provided in parallel to one another at predetermined intervals on an opposite side of the dielectric substrate, characterised in that dielectric leaky wave antenna further comprises: an excitation section having a metal strip for guide which forms a microstrip line between itself and the ground conductor and branching means for branching electromagnetic radiation transmitted in the microstrip line in a direction perpendicular to the plurality of metal strips for leakage (23, 23') in the dielectric substrate, and in that the dielectric substrate is configured to have a lower layer portion and an upper layer portion joined on the lower layer portion, the ground conductor is formed on a lower surface of the lower layer portion of the dielectric substrate, the plurality of metal strips for leakage (23, 23') are formed on an upper surface of the upper layer portion of the dielectric substrate, and the metal strip for guide and the branching means which configure the excitation section are formed between the lower layer portion and the upper layer portion of the dielectric substrate. a dielectric substrate; a ground conductor provided on one surface side of the dielectric substrate, the ground conductor forming a dielectric image guide which propagates electromagnetic radiation in a direction perpendicular to a thickness direction in the dielectric substrate; and a plurality of metal strips for leakage (23, 23') provided in parallel to one another at predetermined intervals on an opposite side of the dielectric substrate, characterised in that dielectric leaky wave antenna further comprises: an excitation section having a metal strip for guide which forms a microstrip line between itself and the ground conductor and branching means for branching electromagnetic radiation transmitted in the microstrip line in a direction perpendicular to the plurality of metal strips for leakage (23, 23') in the dielectric substrate, and in that the dielectric substrate is configured to have a lower layer portion and an upper layer portion joined on the lower layer portion, the ground conductor is formed on a lower surface of the lower layer portion of the dielectric substrate, the plurality of metal strips for leakage (23, 23') are formed on an upper surface of the upper layer portion of the dielectric substrate, and the metal strip for guide and the branching means which configure the excitation section are formed between the lower layer portion and the upper layer portion of the dielectric substrate. an excitation section having a metal strip for guide which forms a microstrip line between itself and the ground conductor and branching means for branching electromagnetic radiation transmitted in the microstrip line in a direction perpendicular to the plurality of metal strips for leakage (23, 23') in the dielectric substrate, and in that the dielectric substrate is configured to have a lower layer portion and an upper layer portion joined on the lower layer portion, the ground conductor is formed on a lower surface of the lower layer portion of the dielectric substrate, the plurality of metal strips for leakage (23, 23') are formed on an upper surface of the upper layer portion of the dielectric substrate, and the metal strip for guide and the branching means which configure the excitation section are formed between the lower layer portion and the upper layer portion of the dielectric substrate.