An apparatus for measuring an electrical potential of retina is provided which is capable of reducing a noise signal in measuring an electrical potential of retina by using electrodes of eyeball-non-contact type and accurately measuring an electrical potential of retina. Fluctuation in electrical potential of retina occurring due to a light stimulus given to one of the left and right eyes of a subject is detected by a corresponding electrode of eyeball-non-contact type, and at the same time, a potential of the other eye that is not light-stimulated is detected by a corresponding electrode of eyeball-non-contact type. Then, a difference between two potential detection signals detected at the same time is found and obtained as a recording signal of electrical potential of retina. Based on this recording signal of electrical potential of retina, a waveform of electrical potential of retina of the light-stimulated eye is found and recorded as an electroretinogram.