Provided are an integrating sphere photometer and a measuring method of the same. The integrating sphere photometer includes an integrating sphere including a left hemisphere and a right hemisphere, a photometer disposed on the center surface of the right hemisphere, a photometer baffle disposed in front of the photometer to be spaced apart therefrom, a light source to be tested disposed at the center region of the integrating sphere to illuminate light to at least an illumination region of the left hemisphere, an auxiliary lamp part disposed in the vicinity of a contact region between the left hemisphere and the right hemisphere to illuminate light to the illumination region, and an auxiliary lamp baffle disposed around the auxiliary lamp part to prevent the light emitted from the light source to be tested from being directly illuminated to the auxiliary lamp part and also to prevent the light emitted from the auxiliary lamp part from being directly illuminated to the light source to be tested.