One or more embodiments provide medical tool grip mechanism to which multiple types of medical instruments can be attached. A grip mechanism grips an instrument. The instrument has a shaft extending in a longitudinal direction, a treatment tool arranged at a distal end of the shaft, and a treatment tool control portion that is arranged at a proximal end of the shaft and controls the treatment tool. The grip mechanism has a gripping portion. The gripping portion grips the treatment tool control portion such that the treatment tool control portion is rotatable about a rotational axis extending in the longitudinal direction of the shaft, and movable in the longitudinal direction with respect to the shaft.