A biological brain age is calculated by measuring a brain cortex thickness of each region in a brain MRI image of a person to be examined, and comparing the measured brain cortex thickness with normal control group information. A device for calculating the biological brain includes an image information input unit to input an MRI brain image of a person to be examined, a brain age calculation control unit to control a biological brain age calculation operation of the person to be examined based on the MRI brain image, a brain thickness measuring unit to measure a brain cortex thickness of each region in the MRI brain image, and a brain age calculating unit to match the measured brain cortex thickness with a normal range of brain thickness of each age, and calculate a biological brain age of the person to be examined.