PURPOSE: To prevent a dielectric rod from being fallen off even when the horn is used in any attitude of position by inserting the dielectric rod inside a corrugated waveguide with a slot of a specific size provided thereto and inserting a part of the dielectric rod inside the slot so as to form a dielectric body.

CONSTITUTION: Plural slots 1a, 1b whose depth is a half wavelength of the operating frequency or below and 1/4 wavelength or over and whose pitch is one wavelength or below are provided to a corrugated waveguide 2 on the inner wall of a circular waveguide 8. Moreover, a dielectric rod 4 is provided, which is prolonged from the inside of the waveguide 2 to the outside and whose diameter or thickness is gradually decreased toward the radiation direction of a radio wave. Then part of the dielectric rod is fitted to the plural slots to form the dielectric body. The radio wave propagating in the inside of the circular waveguide 8 is matched in a wave of the EF11 mode propagated in the corrugated waveguide whose inside is packed with the dielectric body at the matching part 11 and the rear end tapered part 10. Thus, the dielectric focus horn with a low voltage standing wave ratio(VSWR) and an excellent characteristic is realized.