An access port is fixed to a biological membrane, such as the pericardium, in a state in which it penetrates the biological membrane. Provided is an access port including an inner tube and an outer tube fitted together so as to be movable relative to each other in an axial direction, wherein at least one of the inner tube and the outer tube has holding surfaces having substantially complementary shapes that are brought close to or away from each other by relative movement of the inner tube and the outer tube.