A remote-controlled actuator includes a spindle guide section of an elongated shape, a distal end member fitted to a distal end of the spindle guide section for alteration in attitude and rotatably supporting a tool, and a drive unit housing having a base end of the spindle guide section connected therewith. A rotary shaft for transmitting rotation of a tool rotation drive source within the drive unit housing to the tool and an attitude altering member for altering the attitude of the distal end member by the drive of an attitude altering drive source within the drive unit housing are accommodated within the spindle guide section. A cutting force estimator is provided for estimating the magnitude of at least one component force of a principle force, a radial force and a feed force in a cutting force which the tool applies to a work to be processed.