A drainage tube retainer 1 as an endoscopic treatment instrument includes a guide catheter 10 for slidably supporting a drainage tube 6 retained in a live organ through a channel a pusher tube 11 disposed in the exterior of the guide catheter 10 and slidably supported by the guide catheter 10 and a pusher cap 13 provided to the pusher tube 11 for positioning the pusher tube 11 relative to the endoscope so that a direction in which the pusher tube 11 is inserted through the channel substantially coincides with a direction in which the guide catheter 10 is retracted from the pusher tube 11.
