A pipeline closing apparatus comprises a lid member attachable to a downstream end portion of a sluice valve, a first control shaft extending through the lid member, a second control shaft extending through the first control shaft, an elastic annular member disposed between pressing plates and provided on inward end regions of the control shafts and elastically deformable to a diameter-increased position by being clamped and pressed, thereby to block between an inner peripheral surface of a branch pipe and the pressing plates, and a retaining device. The retaining device includes engaging link pairs flexing and bulging to a diameter-increased position in response to outward sliding movement of the second control shaft relative to the first control shaft. The apparatus further comprises a reversal preventing device F which, contacts and limits the engaging link pairs and to an outwardly bent position where flexing pivotal portions of the engaging link pairs project radially outward.