During mountain tunnel construction, it is important to quickly and quantitatively evaluate the mechanical properties of rock for rational and safe excavation. Recently, several methods have been used to quantitatively asses rock hardness by analyzing perforation data from drill jumbos in medium-hard to harder rocks where blasting is used for excavation. On the other hand, there are currently no methods to quantitatively evaluate rock strength in soft rock and sandy mountains where rock breakers are generally used for excavation. Thus, the authors of this study aim to develop an evaluation method to quickly and quantitatively measure strength in softer rock mass. The authors proposed the use of vibration acceleration and sound pressure generated by rock breakers during excavation and verified the feasibility of this approach by performing laboratory tests on concrete specimens. Finally, the authors applied this measurement technique on rock masses of varying strengths and verified that this method is able to quantitatively evaluate rock strength. This paper presents the findings of this study.