Here, the three problems as to the application of the method of experimental education are discussed. First, to what extent have children of 3, 4 and 5 years of age mastered the number? Second, what are the opinions and attitudes of the subjects' parents concerning the number education and how are they teaching the number concept to their children at home? Third, what is the effect of the number education give by the parents? It is shown in our research that the number abilities or performances of the subjects are generally higher than we ordinarilly expect. But, there are also some inconsistencies between various areas of their number abilities. That, is, the tasks of counting, enumeration, writing the number, number identification, number calculation (plus or minus) are much more easily performed than the tasks, seriation, identification of the number of collections, one to one correspondence between two collections. Further, we know that the subjects' parents (belonging to the uppér middle class) are not only eager for high performance of their children of the number operations, but also they are teaching eagerly various number operations, especially, the former sort of tasks. Piaget considers in his “épistémologie génétique” that the establishment of number concept depends upon the discovery of the principles of the conservation