An iris authentication apparatus includes an iris area extraction unit, registration pattern generating unit, collation pattern generating unit, and collation unit. The iris area extraction unit extracts iris areas from a sensed registration eyeball image and a sensed collation eyeball image. When the iris area extraction unit extracts an iris area from the registration eyeball image, the registration pattern generating unit generates a registration iris pattern image by performing polar coordinate transformation of an image in the extracted iris area. When the iris area extraction unit extracts an iris area from the collation eyeball image, the collation pattern generating unit generates a collation iris pattern image by performing polar coordinate transformation of an image in the extracted iris area. The collation unit collates the registration iris pattern image output from the registration pattern generating unit and the collation iris pattern image output from the collation pattern generating unit on the basis of a correlation therebetween.