1. A biometric authentication device which performs biometric authentication of a user using a biometric image in which an object carrying biometric information of the user is photographed, comprising: an illumination light source which illuminates the object; a sensor which generates a plurality of illumination images in which the object is photographed in a state where the illumination light source is turned on, and at least one non-illumination image in which the object is photographed in a state where the illumination light source is turned off; at least one processor configured to: generate a plurality of difference images by subtracting from a luminance value of each pixel of each illumination image a luminance value of a corresponding pixel of the non-illumination image, determine an integration number, based on a statistical value of luminance values of a first difference image which represents an amount of noise superimposed on the first difference image among the plurality of difference images, so that the integration number of the difference images increases as an influence of luminance values of the pixels included in at least one region of the first difference image due to the noise superimposed on the first difference image increases, and generate the biometric image by calculating luminance values of respective pixels of the biometric image based on a total of luminance values of the corresponding pixels of the difference images, the number of which is the integration number, among the plurality of difference images.