The electric medical instrument fitting is attached to a medical instrument holding device. The electric medical instrument fitting includes a fitting body, drive units for a plurality of second medical instruments, and an intermediate member. The fitting body has a fitting portion that enables attachment/detachment of a first medical instrument which can be arranged with an observation device and provided with channel holes for inserting treatment instruments, or which is provided with an observation device. The drive units for the second medical instruments can each be detachably connected with each second medical instrument provided with an insertion portion to be inserted into each channel hole, with a treatment portion being provided on the side of a distal end thereof. Each of the drive units for the second medical instruments is provided with a joint driver, an advancing/retreating driver and a rotation driver, for changing the position and the posture of the treatment portion. Each of the drive units for the second medical instruments has a center of gravity set at a predetermined position of a roll axis of the rotation driver, with the position of the roll axis being apart from a fitting surface by a predetermined distance. The intermediate member is arranged at the fitting body which is attached with the plurality of medical instrument drive units, a center of gravity of the entirety being set on an extension line of a center axis of the fitting portion.
