The purpose of this study was to investigate the appearance and function of spontaneous "Kusho" behaviour among Japanese adults. It was defined as writinglike finger movement without any physical and visible trace. In the first experiment, 105 female college students engaged Kanji grapheme integration task(TABLE 1). Subjects were asked to integrate Kanji after presentation of two or three Kanji graphemes. While the subjects were performing in this task, the appearance of "Kusho" and the type of this behaviour were observed. The results showed that 100% of them did "Kusho". And two types of this behaviour were identified such as 1)writing on any parts of body(e.g.knee, palm etc.)with visual monitoring, and 2)as writing in the air without visual monitoring. In the second experiment, using the same task as in experiment 1, the function of "Kusho" behaviour was investigated under three conditions: 1)writing on the white paper with subject's index finger with visual monitoring, 2)writing in the air without visual monitoring, and 3)any "Kusho" behaviour being prohibited. In each condition, Kanji graphemes were presented in a visual or auditory form. 60 subjects engaged in 12 Kanji grapheme integration task which contained 4 types of Kanji pattern(TABLE, 2). Two-way ANOVA(presentation modality: 2× three "kusho" condition)showed two factor's interaction was significant. In the visual presentation, two types of kusho showed highly effect, but in the auditory condition, kusho writing in the air without visual monitoring revealed no effect(FIG.1). From these results, the effect and the nature of "Kusho" behaviour were discussed in the viewpoints of the functional role of motor imagery.