A pneumoperitoneum apparatus comprising: an insufflation gas source for insufflation; an insufflation conduit for pneumoperitoneum, the insufflation conduit being connected to the insufflation gas source and being configured to feed insufflation gas for pneumoperitoneum; an endoscope connection tube that is configured to connect the insufflation conduit for pneumoperitoneum and an endoscope insufflation conduit provided inside an endoscope including an insertion portion; a flow rate sensor provided on the insufflation conduit for the pneumoperitoneum, the flow rate sensor being configured so as to measure an insufflation flow rate as a measured flow rate; a flow rate setting knob configured so as to set the insufflation flow rate measured by the flow rate sensor as an insufflation flow rate suitable for pneumoperitoneum; and an electro-pneumatic proportional valve provided on the insufflation conduit for pneumoperitoneum, the electro-pneumatic proportional valve being configured so as to, if the measured flow rate measured by the flow rate sensor is not equal to the set flow rate, adjust the insufflation flow rate of insufflation to the endoscope insufflation conduit by an adjustment value for the insufflation flow rate; characterized in that the pneumoperitoneum apparatus further comprises: an adjustment value storing section configured so as to, if the measured flow rate measured by the flow rate sensor is equal to the set flow rate, store the adjustment value for the electro-pneumatic proportional valve; and a CPU configured so as to, if the measured flow rate measured by the flow rate sensor is equal to or below a threshold value after the measured flow rate has reached the set flow rate, perform control to set the adjustment value read from the adjustment value storing section for the electro-pneumatic proportional valve. an insufflation gas source for insufflation; an insufflation conduit for pneumoperitoneum, the insufflation conduit being connected to the insufflation gas source and being configured to feed insufflation gas for pneumoperitoneum; an endoscope connection tube that is configured to connect the insufflation conduit for pneumoperitoneum and an endoscope insufflation conduit provided inside an endoscope including an insertion portion; a flow rate sensor provided on the insufflation conduit for the pneumoperitoneum, the flow rate sensor being configured so as to measure an insufflation flow rate as a measured flow rate; a flow rate setting knob configured so as to set the insufflation flow rate measured by the flow rate sensor as an insufflation flow rate suitable for pneumoperitoneum; and an electro-pneumatic proportional valve provided on the insufflation conduit for pneumoperitoneum, the electro-pneumatic proportional valve being configured so as to, if the measured flow rate measured by the flow rate sensor is not equal to the set flow rate, adjust the insufflation flow rate of insufflation to the endoscope insufflation conduit by an adjustment value for the insufflation flow rate; characterized in that the pneumoperitoneum apparatus further comprises: an adjustment value storing section configured so as to, if the measured flow rate measured by the flow rate sensor is equal to the set flow rate, store the adjustment value for the electro-pneumatic proportional valve; and a CPU configured so as to, if the measured flow rate measured by the flow rate sensor is equal to or below a threshold value after the measured flow rate has reached the set flow rate, perform control to set the adjustment value read from the adjustment value storing section for the electro-pneumatic proportional valve. an adjustment value storing section configured so as to, if the measured flow rate measured by the flow rate sensor is equal to the set flow rate, store the adjustment value for the electro-pneumatic proportional valve; and a CPU configured so as to, if the measured flow rate measured by the flow rate sensor is equal to or below a threshold value after the measured flow rate has reached the set flow rate, perform control to set the adjustment value read from the adjustment value storing section for the electro-pneumatic proportional valve.