Main purpose of this paper is to make clear the development of children's spacial cognition from the view point of the perceived amount in the open field. There are many fore-running studies on this theme, however, most of them are done in the experimented laboratories under the condition of limited factors of psychology. The auther tried to study especially on the perceived amount of herizontal and vertical distance which shape basic conception for space in the open field. The investigation made for the children of grade 3 to 6 and 8, concerning their perceived amount on horizontal and vertical distance of 2m, 10m, and some ten meters. The results are follows. In the case of distance of 2m, the correct perceived amount have already been developed at grades 3, both in horizontal and vertical. In the case of 10m, the accuracy of their perceived amount increase with age: in the horizontal distance, the dispersion between grades is small, but they perceived somewhat shorter: on the vertical distance they developed their accuracy at grade 6, and completely at grade 8. The case of some ten meters, the perceived amount on horizontal, distance increased dramatically with grade. At grade 6, they acquire the accuracy on the average and at grade 8, dispersion disappears mostly. However, in the case of vertical, they perceived it somewhat longer, in general. Though their dispersion is large at grade 5, but it diminishes at grade 6, and acquire the exact perceived amount on the vertical distance at grade 5, but it diminishes at grade 8. It is possible to schimatize the results as follows. 1) For children there could be seen the tendency of synchronism in devlopment of perceived amount on horizontal and vertical distance. 2) They develope horizonal cognition more easily than vertical one. 3) In the case of horizontal distance, they are apt to perceive it shorter than actual distance, and in vertical case, they perceive it longer and also the error is larger in general. 4) Perceived amount develope speedily at grade 5 and 6, and their development is sufficiently achieved at grade 8, on both horizontal and vertical distance.