Due to an increasing number of dementia patients, the development of a rapid and sensitive method for cognitive assessment is awaited. Here, we examined the usefulness of a novel and short (3 min) eye tracking device to evaluate the cognitive function of normal control (NC, n = 52), mild cognitive impairment (MCI, n = 52), and Alzheimer's disease (AD, n = 70) subjects. Eye tracking total score declined significantly in MCI (**p < 0.01 vs NC) and AD (**p < 0.01 vs NC, ##p < 0.01 vs MCI), and correlated well with the mini-mental state examination (MMSE) score (r = 0.57, *p < 0.05). Furthermore, the eye tracking test, especially memory and deductive reasoning tasks, effectively discriminated NC, MCI and AD. The present novel eye tracking test clearly discriminated cognitive functions among NC, MCI, and AD subjects, thereby providing an advantage for the early detection of MCI and AD in screening.