An eyeball detection unit of the present disclosure includes an irradiator that projects substantially parallel illumination light toward a cornea of an eyeball, a detector that detects light intensity of reflected light from the cornea, and a detection controller that identifies a centroid offset in an angular direction of the light intensity of the reflected light from the cornea with respect to a reference optical axis on the basis of a detected value by the detector, and thereafter calculates a positional offset of a cornea position with respect to the reference optical axis.