PURPOSE: To automate the manufacture of dies by performing coordinate transformation of a difference between the coordinate center of an inner and an outer dies and the coordinate center of a installing position in a program, then machining reference holes by electric discharge, and aligning the holes to assemble the dies.

CONSTITUTION: An inlet 3, a fitting and joining faces with an outer die, and a reference face 1c are formed on a stock of an inner die 1. Then the stock is heat treated and the fitting, joining, and reference faces are ground after machining a through hole 2 and an escape hole 9, etc. The stock is set on a table of a CNC electric discharge diesinking machine, an electrode is brought into contact with the peripheral reference face 1c, and the coordinate center of the inner die 1 is decided by arithmetic processing by a CNC device. If a difference between the above coordinate center position and a coordinate center inputted to the CNC device is found, coordinate transformation is performed and then electric discharge machining is performed with the unchanged putting condition of a reference hole 7, bearing face 5a, and escape slope 6a on the table to finish machining of the die 1. In the same manner, an outer die 4 is machined and then the dies 1, 4 are assembled.