We develop an intelligent tutoring system on learners' answers to problems in case-based e-learning. A facilitator instantiates answers and tutoring advice as a tutoring rule preliminary, and the system automatically identifies an appropriate instantiated answer which corresponds to the input sentence of an answer from the learner. Although various kinds of tutoring rules are given on a certain problem, the instantiated answers are very similar to each other among tutoring rules, even if tutoring rules are different. So the input sentence is similar to the wrong instantiated answer of the tutoring rule, which makes it difficult to select the tutoring rule correctly. The proposed method selects the tutoring rule for the input sentence by machine learning of selecting the tutoring rules with the multi-class SVM (Support Vector Machine). The experimental result shows that the proposed method can improve the accuracy of selecting tutoring rules by 21% compared to the method that selects the most similar instantiated answer.