A controller for a contact mechanism for preventing a lack of a pressing force applied from a contacting member to a contacted member when determining a control input to an actuator moving the contacting member by a position control. The controller sets a target position of the contacting member, grasps an actual position of the contacting member, determines a control input to the actuator (so as to increase an output of the actuator along with an increase in a difference between the target position and the actual position of the contacting member to eliminate the difference), and detects that the contacting member contacts the contacted member.