For the purpose of finding out whether the cognition and the judgement of a miscellaneous vessel has been clarifying or not, a investigation on small power-driven vessels was practised in Nagoya-Ko and following results were obtained. 1. They only use the definition in Law and do not use the practical sense of seamen as a standard for above mentioned cognition and judgement, in practical affairs, 2. A tendency that it is safe to give their way to the other, irrespective of whether they are aware of themselves as miscellaneous vessels or not, is found. 3. About 40% or more of all cognitions of misecllaneous vessels or vessels other than miscellaneous vessels are nor proper. 4. Large probability of vessel's collisions due to the difference in the opearations mentioned at the main title of this paper, has always been exsting in harbor. 5. Because of dlfficulty in understanding a miscellaneous vessel in practical affairs, it is expected that the Law makes miscellaneous vessels display the specified signals and makes all vessels sure in being aware of a miscellaneous vessel, if the institution of miscellaneous vessels is maintained further.