A blood removal side pressure sensor (37) of the blood removal line, a blood pump (3), an artificial lung (2), a blood supply side pressure sensor (38) and a flow rate sensor (52) of the blood supply line； From the rotation speed (R) of the blood pump (3) and the blood flow rate (Q) measured by the flow rate sensor (52), a discharge pressure (Pr) specific to the blood pump (3) is calculated, and this specific discharge pressure ( Pr) is added with the blood removal pressure (Pv) measured by the blood removal pressure sensor (37) to estimate the pre-artificial lung pressure (Pm) between the blood pump and the artificial lung, and the pre-artificial lung pressure When the numerical value based on the difference between (Pm) and the post-artificial lung pressure (Pa), which is the pressure value measured by the blood-feeding pressure sensor (38), exceeds the required threshold value, the artificial lung is replaced. It is informed that it is time.脱血ラインの脱血側圧力センサ（３７）と、血液ポンプ（３）と、人工肺（２）と、送血ラインの送血側圧力センサ（３８）及び流量センサ（５２）とを備え、血液ポンプ（３）の回転数（Ｒ）と流量センサ（５２）で測定した血液流量（Ｑ）から、血液ポンプ（３）に固有の吐出圧力（Ｐｒ）を算出し、この固有の吐出圧力（Ｐｒ）に、脱血側圧力センサ（３７）で測定した脱血側圧力（Ｐｖ）を加えて、血液ポンプと人工肺との間の人工肺前圧力（Ｐｍ）を推定し、人工肺前圧力（Ｐｍ）と、送血側圧力センサ（３８）で測定した圧力値である人工肺後圧力（Ｐａ）との差異に基づく数値が、所要の閾値を超えたと判断した場合に、人工肺が交換の時期であることを報知する。
