This study investigated the relationship between participants' evaluation of creativiy and characteristics of creative products towards a clear and objective definition of the concept of creativity. Three experiments examined whether the size of "idea search space" in the creative process predicts the score of products in creativity assessments. In Experiment 1, in order to construct an multidimensional scaling (MDS) space which was supposed to correspond to creators' "idea space," 20 participants exhaustively evaluated the strength of semantic connection between every pair of 50 (physical) parts of possible creatures. In Experiment 2, 40 participants drew novel extraterrestrial creatures using five out of 50 parts used in Experiment 1. In Experiment 3, 20 participants assessed the creativity of each of the 40 drawings from Experiment 2. The results showed that a drawing with a larger idea search space estimated by the MDS score have a tendency to receive a higher creativity score. These results support the framework of idea search space and a possibility of explaining the creativity in terms of this model is suggested.