1. A defect classification method of classifying defect images using classification recipes corresponding to a device which photographs a sample and a process in which the sample is manufactured, comprising: a step of defining a same classification class as a classification class defined by a classification recipe of a first image photographing device and by a classification recipe of a second image photographing device corresponding to a same manufacturing process as the classification recipe of the first image photographing device; a step of specifying a defect image of a same type as an instruction image registered in the classification class defined by the classification recipe of the first image photographing device from among defect images photographed by the second image photographing device; and a step of registering the specified defect image in the same classification class as the classification class of the first image photographing device in which the instruction image is registered, among classification classes defined by the classification recipe of the second image photographing device, wherein the specifying step includes a step of converting the instruction image registered in the classification class defined by the classification recipe of the first image photographing device to resemble an image photographed by the second image photographing device.