An adapter for an endoscope (50) of the present invention includes: a locking device for attaching and detaching (52) that attaches and locks this adapter for an endoscope onto a predefined position on an endoscope control part (11) and a first treatment tool locking device (52) that keeps a treatment tool (30) at a first predefined position. Furthermore, at the first predefined position, a guidewire entry aperture (36) of the treatment tool and an entry aperture (15) of a forceps plug (14) are separated in such a way as to face each other along substantially the same line.
