An image generating device which generates a biometric image in which an object carrying biometric information of a 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; a difference image generating unit which generates a plurality of difference images by subtracting from a luminance value of each pixel of each illumination image a luminance value of corresponding pixel of the non-illumination image; a biometric image generating unit which realizes a number determination function calculating at least one of a variance and an average of the luminance values of pixels in an object region, in which the object is captured, in a first difference image among the plurality of difference images, as a statistical value which represents an amount of noise superimposed on the first difference image and determining a first number of the difference images used to generate the biometric image, based on the statistical value, so that the greater the amount of noise superimposed on the first difference image, the greater the first number, and an image integration function generating the biometric image by calculating luminance values of respective pixels of the biometric image based on a sum of luminance values of the corresponding pixels of the first number of difference images among the plurality of difference images, wherein when the statistical value of the luminance values is the variance of the luminance values of pixels, the number determination function calculates a variance of the luminance values of pixels in the object region in the first difference image and determines the first number so that a variance of the luminance values of pixels of the biometric image estimated from the calculated variance of the luminance values and the first number is equal to or less than a predetermined threshold, and when the statistical value of the luminance values is the average value of the luminance values of pixels, the number determination function calculates an average value of the luminance values of pixels in the object region in the first difference image and determines the first number by dividing, by the calculated average value, a reference average value which is an average value of luminance values of pixels in the object region in the reference image which is obtained when the object is photographed in a state where the illumination light source is turned on and there is no environmental light. 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; a difference image generating unit which generates a plurality of difference images by subtracting from a luminance value of each pixel of each illumination image a luminance value of corresponding pixel of the non-illumination image; a biometric image generating unit which realizes a number determination function calculating at least one of a variance and an average of the luminance values of pixels in an object region, in which the object is captured, in a first difference image among the plurality of difference images, as a statistical value which represents an amount of noise superimposed on the first difference image and determining a first number of the difference images used to generate the biometric image, based on the statistical value, so that the greater the amount of noise superimposed on the first difference image, the greater the first number, and an image integration function generating the biometric image by calculating luminance values of respective pixels of the biometric image based on a sum of luminance values of the corresponding pixels of the first number of difference images among the plurality of difference images, wherein when the statistical value of the luminance values is the variance of the luminance values of pixels, the number determination function calculates a variance of the luminance values of pixels in the object region in the first difference image and determines the first number so that a variance of the luminance values of pixels of the biometric image estimated from the calculated variance of the luminance values and the first number is equal to or less than a predetermined threshold, and when the statistical value of the luminance values is the average value of the luminance values of pixels, the number determination function calculates an average value of the luminance values of pixels in the object region in the first difference image and determines the first number by dividing, by the calculated average value, a reference average value which is an average value of luminance values of pixels in the object region in the reference image which is obtained when the object is photographed in a state where the illumination light source is turned on and there is no environmental light.