A body cavity internal pressure regulating device is connected to an endoscope including a suction channel used for suction under manual control and a forceps channel used to insert an instrument into a body cavity, and the body cavity internal pressure regulating device regulates a body cavity internal pressure. A gas supply unit performs a gas supply through the forceps channel. A suction detection unit detects that suction is being performed under manual control through the suction channel. A control unit terminates the gas supply being performed by the gas supply unit according to a result of detection by the suction detection unit when the control unit detects that suction is being performed under manual control through the suction channel while the gas supply unit is performing a gas supply.
