Abstract: Scissors on the distal end of a medical instrument are assembled highly accurately for cutting an object with ease. A scissors mechanism is assembled as a unit. The scissors mechanism has a pair of end effector members openably and closably fastened at proximal ends thereof by a bolt and nuts, while being held in a predetermined sliding state. The bolt has a central hole defined axially therethrough. The scissors mechanism is inserted into a tubular structure of a cover, which is coupled to the distal end of a joint shaft, and the end effector members are connected to a driven plate by links. A spacer is placed in a gap between the scissors mechanism and an inner surface of the cover. A pin is inserted, from an outer surface of the cover, into a hole of the cover and the central hole of the bolt.