A wakefulness level determination device includes a processor and a memory. The processor executes: calculating a first feature value from a heartbeat signal of a subject estimating, from the first feature value calculated at the calculating, a feature value of the subject when not fully awake on the basis of a correlation between a feature value of a heartbeat signal of a person fully waking and a feature value of a heartbeat signal of a person not fully waking setting, as an index of a wakefulness level, a range from the first feature value calculated at the calculating to the feature value estimated at the estimating calculating a second feature value from a heartbeat signal of the subject and determining a wakefulness level of the subject by comparing the second feature value with the index of the wakefulness level that is set at the setting.
