PURPOSE: To omit the adjustment that is needed for attachment of a subsidiary reflection mirror support mechanism to an attachment plate.

CONSTITUTION: In regard of a subsidiary reflection mirror support mechanism of an antenna device which position and holds the subsidiary reflection mirror at a prescribed position to a principal reflection mirror, the reinforcing members 29 and 30 are provided on the rear face of the principal reflection mirror. Then an attachment plate 41 set in the same direction as the rear face of the principal reflection mirror is fixed to the members 29 and 30 by an adhesive 44. This adhesive 44 absorbs the tilt caused between the plate 41 and the members 29 and 30. A flange 42 is formed to a support member 43 which supports the subsidiary reflection mirror. Then the flange 42 is adhered to the plate 41 and fixed there by a bolt 45 and a nut 46. A tilt washer 47 is put between the nut 4 and the members 29 and 30 to absorb the tilts of each reinforcing member.