A. Bain's academic activities were chronologically reviewed, followed by a discussion of the historical significance of his ideas for the modern psychology. Descriptions were also made concerning the introduction of his works to other countries, particularly to Japan at the dawn of her new age. Finally it was stressed that (1) Bain did much to free psychology from me taphysical speculation and to establish it as a positive observational science; (2) His psychology was tending to become more behavioral (functional), comparative, and physiological; and (3) He reached a standpoint that is medium in many dimensions, what means he was really an integrator.