At the Kamioka Mine, the stoping method of main stopes, formerly shrinkage or cut and fill, has been gradually replaced by sub-level stoping method, using long blast holes (radial horizontal holes since 1946, or vertical downward holes). Long blast holes are about 10-15 m in depth and 46 mm' in diameter, blasted by milli-second delay electric detonators.This report describes mining and drilling method and its cost in following chapters:-(1) General geology(2) Process of the study(3) Method of drilling of long hole(4) Method of sub-level stoping(5) Conclusion