PURPOSE: To obtain a well-finished, smooth, excavated surface by providing a plurality of blasting holes at specified space intervals, setting electronically delayed electric detonator caps at specified times and simultaneously effecting blasting in the blasting holes within a specified accuracy of time with regard to the set times.

CONSTITUTION: In a 11-stepped blasting of a cross section of a tunnel, blasting holes H1-H14 on a tenth-step outermost circumference are spaced apart at intervals of 30-100cm. Delay times are set in an accuracy of not more than 1ms by using DS electric detonator caps for the blasting holes H1-H7 located on the left side when viewed from the side facing a cutting face and electronically delayed electric detonator caps of a high time accuracy for the other blasting holes H8-H14 on the right side. Because damages of bedrock are suppressed and a straight, smoothly finished surface is obtained, overbreak, unfixed stone removing work and hindering stone removing work in assembling supporting are reduced.