1. A medical system, comprising: a slave medical treatment tool to be controlled and including a first shaft coupled to a first grip grasped by a user, a first end effector located at a distal end of the first shaft, a moving joint for adjusting an angle of the first end effector relative to the first shaft, and a driver for driving the moving joint; a master medical instrument serving as a master control instrument and including a second shaft coupled to a second grip grasped by the user and a second end effector located at a distal end of the second shaft; a first trocar having an insertion opening through which the slave medical treatment tool is inserted; a second trocar having an insertion opening through which the master medical instrument is inserted; a sensor for producing out a sensor signal including at least an angle of the second effector; and a controller that sets a follow-up criterion based on a sensor signal produced out of the sensor and enables follow-up processing for driving the driver such that an angle of the first end effector follows the follow-up criterion.