Provided is a unit used in a surgical operation using an endoscope, for example, to position the distal end of a surgical instrument to the region of a human body where medical treatment is required, without spreading a hole formed in the human body for insertion of the surgical instrument. This unit includes first and second output shafts pivotally connected to a movable member of the surgical instrument or the like, the first and second output shafts extending parallel to each other and being capable of reciprocating, and a drive unit for giving the first output shaft an arbitrary amount of advance/retraction and constantly giving the second output shaft an amount of advance/retraction of a constant ratio (≠1) with respect to the amount of advance/retraction given to the first output shaft.