PURPOSE: To improve even the measuring accuracy with a measuring process simplified and the time for measurement shortened by using a magne-scale type position detecting device as the means detecting height of a Z-axis.

CONSTITUTION: An upper part wire electrode guide 18 is able to move in a vertical direction along a Z-axis base 21, supported to a column 12, and supported to the bottom end of a Z-axis 22. This Z-axis 22 vertically moves being supported to a lead screw 23 provided along the Z-axis 22 and rotated by rotating a handle 24. This Z-axis position detecting device 3 mounts its magne-scale main unit 31 to the Z-axis 22, magne-scale read part 32 to the Z-axis base 21 and a display part 33 to a control panel or the like not shown. By the constitution thus obtained, a process of measuring a position of the upper part electrode guide 18 is simplified, and the time for measurement of the position is shortened, further measuring accuracy can be extremely improved.