PURPOSE: To make orifice in the side of a small-diameter tube such as a dripping needle by correcting the shape of grindstone all the time under process in such a manner that a uniform orifice configration can be obtained.

CONSTITUTION: A grinding wheel 14 operated by a motor is put into touch with a diamond electrophoretic shaping grindstone 15 provided with a required shaping gutter 16, which makes correction of the outside configuration of grinding wheel 14. An orifice 17 is excavated by pressing this grinding wheel which underwent the correction processing, against the small-diameter tube 11 at the requested point. The grinding wheel 14 shall undergo the above-mentioned correction process after excavating an orifice and before proceeding to the next cycle of work to secure a uniform orifice configuration always. The arrangement required is such that the shaping gutter 16 in the shaping grindstone 15 is situated at the same level as the lower end of grinding wheel 14, which shall be a little lower than the top end of the small-diameter tube 11.