Problem: It is the purpose of this study to analyse play-situations from the point of view of the substitute action.Experiments: At first, I experimented in the situation of playing with a doll. During the play, when the subject (5;0-6;5, girls) fed the doll with chocolate (original thing), I gave her a piece of cardboard (substitute), in order to observe whether the subjects accepted the cardboard or not as the substitute of the chocolate.The results were that the cardboard was accepted almost 100% as chocolate. According to this result, this play-situation seems to be so free that anything in it is easily substituted. But it is a question whether in all play-situations the substitutions are so free or not as in the situation of playing with a doll.Accordingly, I attempted the next experiment in the situation of throwing a ball. In this experiment, the gum orange, newspaper etc. (substitutes) were anyhow accepted as the substitutes of the ball (original thing). However, in the situation of the competitive throwing of a ball, those substitutes were refused to be taken in 40% of cases.From the results of these experiments, it seems to me that the play-situations are not always so free with regard to substitution as in the situation of the playing with a doll. Then what are the distinctive characteristics of these two cases? In one case, for instance in the situation of the competitive throwing of a ball, the aim is definitely settled then the substitution is difficult. But in the other, for instance in the situation of playing with a doll or throwing of a ball, the aims are so ambiguous that the substitutes are easily accepted.In order to test this assumption, I experimented in the situation of playing with a toy-car. If the assumption be true, it is expected that in the situation in which the car runs on the rails, the aim is settled more definitely than in the free situation without rails, and accordingly the substitution should be more difficult in the former than in the latter. The results showed that in the situation with rails the substituted cases were only 18% of all cases, while in the situation without rails they were 63%.Summary: 1) As far as seen from the point of view of the substitute action, it seems that the play-situations in which the aims are definitely settled are functionally distinguished from the play-situations in which the aims are ambiguous.2) In the situations in which the aims are ambiguous, the substitution is influenced by the degree of the development of the situations and intelligence, and the qualities of substitutes.3) In the situations in which the aims are definite, the substitution is influenced by the degree of the development of the situations and the consciousness on the meanings of the plays.