A medical operation device is attachable to an insertion portion of a medical instrument for observation. The medical operation device includes: rotary cylinder rotatably disposed in device main body that has insertion portion inserting hole through which insertion portion is inserted; insertion portion pressing member that presses insertion portion inside rotary cylinder; insertion portion mounting section cover provided inside insertion portion inserting hole that prevents insertion portion directly touching inner face of insertion portion inserting hole, vicinity of opening of insertion portion inserting hole, and insertion portion pressing member; switching instruction portion that switches whether insertion portion pressing member presses insertion portion to specify state where rotary cylinder and insertion portion are united and state where insertion portion moves forward/rearward with respect to rotary cylinder; and rotation mechanism that, when rotary cylinder and insertion portion are united, rotates rotary cylinder to rotate insertion portion unified with rotary cylinder around insertion portion axis.