A hydraulic forceps system includes: robotic forceps including: a gripper, first piston coupled to the gripper, first cylinder forming first pressure chamber, filled with a hydraulic fluid, together with the first piston, second piston, second cylinder forming a second pressure chamber, filled with hydraulic fluid, together with the second piston, communication passage through which the chambers communicate, motor that drives the second piston via a linear motion mechanism； control device that controls the motor based on a command position for the first piston； and position sensor used for detecting a position of the second piston. The control device includes: an observer that derives an estimated position of the first piston based on the position of the second detected by the sensor； and a position controller that derives a target rotational speed of the motor based on a deviation between the estimated position of the first piston and the command position.
