An object of the invention is to provide for automatic angular adjustment of an end effector thereby improving on the operability of a medical instrument. The medical system of the invention comprises a medical instrument including a driver for driving adjustment of the angle of the end effector relative to a shaft, a trocar having an insertion opening through which the medical instrument is inserted, a sensor that produces a sensor signal including at least an angle of a shaft in a reference coordinate system, and a driver for enabling follow-up control processing for driving the driver based on a sensor signal produced out of the sensor such that the angle of the end effector follows a follow-up criterion in a reference coordinate system.
