An apparatus includes an endoscope and a surgical instrument guide device. An elongated surgical instrument is allowed to insert through a working channel of the endoscope to cooperate with a processor module of the endoscope. The surgical instrument guide device includes a base member, an adjustment member, a catch, a cap member, fasteners, and a tubing. Pegs of the catch are fitted in positioning holes of the base member. A tube of the endoscope is inserted through the tubing of the surgical instrument guide device so as to dispose in close proximity to a target.
