Slope failure resulting from heavy rainfall on railway lines is a common occurrence, making it essential to minimize the phenomenon in the interests of maintaining safe, punctual train operation. It is also necessary to evaluate the disaster risk of individual slopes by considering the probability and potential cost of rainfall-related slope failure. We developed a method to evaluate the potential for slope collapse using a risk assessment technique. This paper describes the method of priority determination for investment to prevent slope failure caused by intense rainfall through application of the technique developed.