A computer (30) obtains a facial image acquired by picking up an image of a person subjected to image pickup from a camera (10), and estimates a facial expression of the person subjected to image pickup based on the obtained facial image. Next, the computer obtains an eye open level of the person subjected to image pickup based on the facial image, and sets a threshold of the eye open level based on the estimated facial expression of the person subjected to image pickup. When the eye open level exceeds the threshold, the computer (30) determines that the eye of the person subjected to image pickup is opened. Moreover, when the eye open level does not exceed the threshold, the computer determines that the eye of the person subjected to image pickup is closed.
