PURPOSE: To improve the fine parts positioning precision by connecting one end of a two-node link member to a motor and a micrometer head and fitting an adjusting bar to the other end.

CONSTITUTION: An adjusting bar 5 pushes a head base 2, is connected to a two- node link member 7, and is further connected to a micrometer head 8. The head 8 is connected to a stepping motor 9 with a coupling 10. A slide base 13 is moved up and down by a motor 15 with a gear head 14, and a coupling 16 connects the rotary shaft of a gear head 14 to a ball screw 17. The motor 15 is driven, the slide base 13 and adjusting bar 5 are raised, an upper drum 1 is fixed to an oil pressure mandrel 6, then the motor 15 is driven, and the adjusting bar 5 is inserted into the adjusting hole 4 on the upper drum 1. Next, a motor 9 is driven, the spindle of the head 8 is protruded or withdrawn, and a base 2 is pushed by the bar for positioning.