1. A cognitive impairment determination apparatus comprising: a data acquisition section that acquires vital signal data at each of predetermined brain locations, for a test subject whose level of cognitive impairment is unknown, measured whilst the test subject is being given a task that causes brain activation; a characteristic amount extraction section that extracts a plurality of vital characteristic amounts from the respective vital signal data of the test subject of the unknown cognitive impairment level acquired by the data acquisition section; and a determination section that determines a level of cognitive impairment of the test subject of the unknown cognitive impairment level based on (1) at least one determination characteristic amount configured from a combination of a brain location and a vital characteristic amount of the vital signal data of the brain location, for use in determining a level of cognitive impairment, pre-selected based on (a) the plurality of vital characteristic amounts extracted respectively from vital signal data at each of the predetermined brain locations of a plurality of test subjects whose level of the cognitive impairment is known, and (b) levels of cognitive impairment of each test subject, wherein the determination characteristic amount is obtained from the plurality of vital characteristic amounts of the respective vital signal data of each of the brain locations of the test subject extracted by the characteristic amount extraction section, and (2) a model for determining the cognitive impairment level corresponding to the determination characteristic amount, the model being pre-built using as learning data (a) the selected determination characteristic amounts for each of the plurality of test subjects, as obtained from the plurality of vital characteristic amounts of the respective extracted vital signal data of each of the brain locations of the plurality of test subjects, and (b) the respective cognitive impairment levels of each of the plurality of test subjects.