The present study attempted to measure a kind of writing ability. In order to reduce the individual variations of better basic language skills, a story production task was given to 153 junior and senior high school students. They were shown a picture which had been picked up from a picture book and were asked to make essays the picture would inspire them. It was required that they should make stories supposed to be read aloud to 1st grade children of elementary school by their mothers. In order to keep high quality of evaluation, essays were rated by 7 experts. The reliability coefficients based on the generalizability theory showed quite reasonable values. The path diagram showed that the effects of the basic language skills to the quality of essays could be ignored, but that the emotional factors on writing and reading, and voluntary habit of writing in a daily life had significant effects. Moreover, it was suggested that favourable experiences on books in preschool period had an influence on cultivating a positive emotional attitude on writing and reading, but compulsory trainings for writing had nothing to do with other factors.