To appropriately determine a state of a target person from a change in a pupil diameter.SOLUTION: A state determination device (100, 200) is capable of performing a state determination process for determining a state of a target person based on a change in a pupil diameter of the target person due to light emitted toward the target person. The state determination device is comprised of: estimating means (23, 11) for estimating brightness around the target person； and determination means (11) for performing at least one of (i) determination of whether or not to determine a state of the target person by a state determination process, and (ii) determination of determination criteria in the state determination processing based on the a difference between brightness of light emitted toward the target person and the estimated brightness.SELECTED DRAWING: Figure 1【課題】瞳孔径の変化から対象者の状態を適切に判定する。【解決手段】状態判定装置（１００、２００）は、対象者に向けて発せられた光に起因する対象者の瞳孔径の変化に基づいて対象者の状態を判定する状態判定処理を実施可能な状態判定装置である。当該状態判定装置は、対象者の周囲の明るさを推定する推定手段（２３、１１）と、対象者に向けて発せられた光の明るさと、推定された明るさとの差に基づいて、（ｉ）状態判定処理により対象者の状態を判定するか否かの決定、及び、（ｉｉ）状態判定処理における判定基準の決定、の少なくとも一方を行う決定手段（１１）と、を備える。【選択図】図１
