The purpose of this study is to collect the fundamental data on the children's probability concept which provide information for teachers and other developers of curriculum. We apply two kinds of problems for the achievement of this purpose. One is the comparison problem which compares probabilities of a pair of events. And the other one is the rating problem which rate the probalibility of events on the line segment a dot. We adopt a lottery as a discrete event and a roulette as a continuous event. As a rerult of this study, we find out the flollowing: 1)The variables of event, namely, the size, difference and change of the numbers of balls, and the position, proportion and partition of a rourellte boards influence children's subjective judgement of likelihood of events. 2)It is more difficult for childrens to grasp the continuous events than the discrete events. 3)The rates of correct answer of the both problems are improved gradually as to age. Esprcially, the performange of sixth grader are better than lower grader. This suggests us that the learning of "Circle", "Proprotion", and "Ratio" is related to the improvement in the understanding of likelihood of events.