This system for in-body-cavity liquid perfusion of a circulating type (10), which circulates a liquid such as an isotonic solution perfused within the body cavity, suppresses an excessive increase in internal pressure that would lead to breakage of a hollow fiber membrane module (20). A drain valve (62) is connected to a drain port (60) of the hollow fiber membrane module (20). A pressure sensor (28, 32) measures the internal pressure of the hollow fiber membrane module (20). A control unit (21) opens the drain valve (62) on the basis of the internal pressure of the hollow fiber membrane module (20) measured by the pressure sensor (28, 32), draining foreign matter from the hollow fiber membrane.
