A remote controlled actuator which comprises: a spindle guide section of an elongated shape; a distal end member fitted to a tip of the spindle guide section through a distal end member connecting unit for alteration in orientation; a tool rotatably provided in the distal end member; a tool rotation drive source for rotating the tool; an orientation altering drive source for operating the orientation of the distal end member; and a drive unit housing to which a base end of the spindle guide section is connected, in which the distal end member rotatably supports a spindle for holding the tool, in which the spindle guide section has its interior accommodating a rotary shaft for transmitting a rotation of the tool rotation drive source to the spindle and a guide hole having its opposite ends opening, in which a flexible orientation altering member is reciprocally movably inserted within the guide hole, and has a tip for undergoing a reciprocating or retracting motion in contact with the distal end member so as to alter the orientation of the distal end member, the orientation altering member being selectively advanced or retracted by the orientation altering drive source; further comprising a position detector for detecting an advanced or retracted position of the orientation altering member from a site separate from the orientation altering drive source; and further comprising a force increasing and transmitting mechanism provided within the drive unit housing and comprised of a lever mechanism for increasing and transmitting an output of a direct acting member, which is selectively advanced or retracted by the orientation altering drive source in a linear direction, to the orientation altering member, and in which the position detector comprises a displacement amount measuring unit for measuring the amount of displacement of a lever of the force increasing and transmitting mechanism, and a displacement amount estimator for estimating the advanced or retracted position of the orientation altering member from a measured value of the displacement amount measuring unit. a spindle guide section of an elongated shape; a distal end member fitted to a tip of the spindle guide section through a distal end member connecting unit for alteration in orientation; a tool rotatably provided in the distal end member; a tool rotation drive source for rotating the tool; an orientation altering drive source for operating the orientation of the distal end member; and a drive unit housing to which a base end of the spindle guide section is connected, in which the distal end member rotatably supports a spindle for holding the tool, in which the spindle guide section has its interior accommodating a rotary shaft for transmitting a rotation of the tool rotation drive source to the spindle and a guide hole having its opposite ends opening, in which a flexible orientation altering member is reciprocally movably inserted within the guide hole, and has a tip for undergoing a reciprocating or retracting motion in contact with the distal end member so as to alter the orientation of the distal end member, the orientation altering member being selectively advanced or retracted by the orientation altering drive source; further comprising a position detector for detecting an advanced or retracted position of the orientation altering member from a site separate from the orientation altering drive source; and further comprising a force increasing and transmitting mechanism provided within the drive unit housing and comprised of a lever mechanism for increasing and transmitting an output of a direct acting member, which is selectively advanced or retracted by the orientation altering drive source in a linear direction, to the orientation altering member, and in which the position detector comprises a displacement amount measuring unit for measuring the amount of displacement of a lever of the force increasing and transmitting mechanism, and a displacement amount estimator for estimating the advanced or retracted position of the orientation altering member from a measured value of the displacement amount measuring unit.