Abstract: An access device used with an endoscope includes an access pipe configured to be inserted into a sheath of the endoscope, a piercer disposed on a distal end portion of the access pipe and configured to pierce into a hollow organ through a digestive tract of a patient, and a treatment tool configured to be inserted into the access pipe and to be introduced into the hollow organ by the piercer. The access device is switchable between a first configuration and a second configuration. In the first configuration, a piercing function of the piercer is switched on, so that the piercer pierces the digestive tract and the hollow organ to enter into an interior of the hollow organ, and in the second configuration, the piercing function of the piercer is switched off, the piercer is kept connected to the interior of the hollow organ.