A remote-controlled actuator assembly includes a distal end member fitted to a tip end of a spindle guide section for alteration in attitude, a tool rotatably provided in the distal end member, a tool rotation drive source for rotating the tool, and an attitude altering drive source for operating the attitude of the distal end member. The spindle guide section has a rotary shaft for transmitting a rotation of the tool rotation drive source to the spindle and an attitude altering member to alter the attitude of the distal end member. The attitude altering drive source includes a reduction unit to reduce a speed of input rotation from the attitude altering drive source, a motion converter mechanism to convert a rotational output from the reduction unit to advance/retraction motion, and an output member to cause the attitude altering member to advance/retract according to an output of the motion converter mechanism.