Piaget, J. et al. (1960) suggested that the number of segments (elements) of two lines might influence the judgement of their lengths at a certain level, although its role was equivocal. And then they said that the youngest subjects lacked the concept of number so that their judgements of length were not influenced by the number of segments. The present study was aimed at investigating their suggestions. systematically, including development of number, with a hundred children from three to eight years old. The children were given the six tasks individually.) Counting objects. 2) Taking out the given number of an aggre-gate. 3) Courparison of two number words. 4) Conservation of number. 5) Comparison of length-A (Conservation of length,earranging matches at right angles to one another and in a series of zigzags.) 6) Comparison of length-B (using two straight strips of paper, each having different number of segments.)