A servomotor control device includes: a servomotor; a driven body that is driven by the servomotor; a connection mechanism that connects the servomotor and the driven body; a first position detection section that detects a position of the servomotor; a second position detection section that detects a position of the driven body; and a motor control unit, in which the motor control unit includes: a force estimation section that estimates a drive force acting on the driven body at a connection part between the connection mechanism and the driven body; a rigidity estimation section that estimates a magnitude of rigidity of the connection mechanism based on a detected position of the servomotor, a detected position of the driven body, and an estimated drive force; and a rigidity variation detection section that detects a change in rigidity of the connection mechanism, based on the estimated magnitude of rigidity.