The present invention relates to a method of measuring anesthesia depth including a step of quantifying the sharpness in the major axis direction of a Poincar plot distribution and a step of evaluating the randomness contained in the electroencephalogram based on the sharpness to judge the depth of anesthesia provide.本発明は、ポワンカレプロット分布の長軸方向への先鋭度を定量化する工程、前記先鋭度に基づき脳波に含まれる乱雑性を評価して麻酔深度を判定する工程を含む、麻酔深度測定法を提供する。