1. A corneal surgery apparatus ablating a cornea with a laser beam comprising: ablation amount computing means for obtaining an ablation amount of the cornea for each of plural ablation steps based on a refractive error of an eye to be operated; determining means for determining laser irradiation control data for each of the ablation steps based on the ablation amount for each of the ablation steps obtained by the ablation amount computing means; corneal shape measurement means including a projecting optical system for projecting a target for measuring a corneal shape on the cornea, a photographing optical system for photographing an image of corneal reflection of the target projected on the cornea, and shape computing means for obtaining a corneal shape by processing the photographed target image; and correcting means for comparing a predetermined ablation amount with an actual ablation amount for a certain ablation step based on the corneal shape measured after laser irradiation at the ablation step and for correcting the laser irradiation control data for a next ablation step based on a result of the comparison.