The purpose of this study is to analyse the child's conception of number from two aspects, one is the magnitude of the number and the other is a set of tasks which are given under diLferent stimulus condition. The number 1, 2, 3, 4, 5, 6, 8, and 10 are used. And the tasks used are as follows. ( I ) Comparative judgement of the number of the two aggregates which comprise the different number of elements or the same number of elements. ( 2 ) Estimation of the number of an aggregate under the diLferent stimulus pattern. ( 3 ) Division of the aggregate into the smaller ones which corhprise the same number of elements. ( 4 ) Construction of the given number of an aggregate out of elements. ( 5 ) Taking into account the change in number of an aggregate produced by the addition and subtraction of an element. ( 6 ) Reproduction of the figures which comprise. a regular pattern, a circular pattern and an irregular pattern with "go" pieces. ( 7 ) Taking into account the change in the number of an aggregate produced by the perceptual change of an aggregate.