A luminal cavity closing device can include a flexible shaft, a lid member, and a detachment mechanism. The flexible shaft extends in an axial direction. The lid member which is attached to a distal end of the shaft, can be rotated according to a torque transmitted from the shaft. Thus, a lock section can be thrust into a periphery of an opening of a luminal cavity formed in a living body lumen, to thereby lock the lid member to the periphery. The detachment mechanism can be configured to detachably attach the lid member to the shaft. The torque can be transmitted to the lid member, and the shaft can be detached from the lid member by the detachment mechanism while the lid member is locked to the periphery of the opening of the luminal cavity.