In the biological information measuring device 1, the internal pressure control unit 30 increases or decreases the internal pressure of the compression band 10 wound around a part of the living body. The time-series data acquisition unit 32 acquires time-series data of the capacity and the internal pressure of the compression band 10 while the internal pressure of the compression band 10 increases or decreases. The relationship deriving unit 34 derives the relationship between the capacity of the compression band 10 and the internal pressure based on the time-series data. The deciding unit 36 derives a first differential value by differentiating the relationship between the capacity and the internal pressure with the internal pressure, derives a second differential value by differentiating the first differential value with time or the internal pressure, and derives the second differential value. Is determined as the blood pressure of the living body. 生体情報測定装置１において、内圧制御部３０は、生体の一部に巻かれた圧迫帯１０の内圧を増加または低下させる。時系列データ取得部３２は、圧迫帯１０の内圧が増加または低下する間、当該圧迫帯１０の容量および内圧の時系列データを取得する。関係導出部３４は、時系列データにもとづいて、圧迫帯１０の容量と内圧の関係を導出する。決定部３６は、容量と内圧の関係を内圧で微分して第１微分値を導出し、当該第１微分値を時間または内圧で微分して第２微分値を導出し、当該第２微分値のピークの内圧を生体の血圧に決定する。
