An electrically-operated chuck opening-closing device includes a chuck that grasps workpiece, a conversion device with a control gear provided to the outer circumference, a drawbar that couples the conversion device and the chuck, a transmission gear provided to a main spindle, a second rotary shaft rotatably pivoted to be parallel to the main spindle, a first gear and a second gear rotatably provided on the second rotary shaft, an auxiliary motor that drives the first gear, a first clutch that can couple and decouple the auxiliary motor and the second rotary shaft, and a second clutch that can couple and decouple the second rotary shaft and the second gear.