A connector includes a housing having a first female-side connecting port, a liquid circulation space, and a male-side connecting section communicating with the liquid circulation space, a first valve disk made of elastic material and having a hollow section and a top slit formed in the top and received in the housing, a pin movably installed in the housing, and an urging section for urging the pin axially. In this connector, the top slit spreads and communication is established between a tube interior and the hollow section, and at the same time the top of the pin is pressed to cause the pin to move axially, enlarging the clearance between the hollow section and the pin, thereby establishing communication between the tube interior and the male-side connecting section interior successively through the top slit, the hollow section and the liquid circulation space.