A body cavity internal pressure regulating device 8 is connected to an endoscope 1 including a suction channel 17 used for suction under manual control and a forceps channel 19 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 24 performs a gas supply through the forceps channel 19. A pressure gauge 21 and a flowmeter 22 detects that suction is being performed under manual control through the suction channel 17. A control circuit 25 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 circuit 25 detects that suction is being performed under manual control through the suction channel 17 while the gas supply unit 24 is performing a gas supply.
