For example, with reference to FIG. 10, in the order of the first, second and third problem, the characteristic of each problem included in a problem set can be displayed on a screen in accumulative manner. Accordingly, the size of the point corresponding to the first and second attributes, which are commonly defined as attribute in all problems, can become larger and larger, and the thickness of the line corresponding to the correlation between the first and second attributes, which are commonly defined as attribute in all problems, can become thicker and thicker.

According to the method for indicating characteristic of problem set according to the third embodiment of the present invention, the characteristic of problem set visually displayed on a screen can be accumulatively indicated, thus a learner or a user can easily and directly understand the frequency of the attributes and the frequency of the correlations between the attributes, which leads to a more precise and easier analysis of the characteristic of problem set.