A medical system includes: an elongated medical device having flexibility； an elongated over-tube having flexibility and having a channel into which the medical device is inserted in a longitudinal direction； a movement mechanism including a slider attached to a proximal end of the medical device, the movement mechanism being configured to move the medical device in the longitudinal direction relative to the over-tube； a wire fixed to a distal end of the over-tube and extending parallel to the channel, the wire being supported in a movable manner only in the longitudinal direction relative to the over-tube； a sensor that detects a protruding length of the wire from the proximal end of the over-tube； and a controller that calculates a path length of the channel based on the protruding length of the wire detected by the sensor.
