Androdioecy is a rare reproductive system. Fraxinus platypoda is a canopy woody species that can reach up to 40 m height in mountainous riparian zones in Japan. This species is morphologically androdioecious with hermaphrodite and male individuals in the population. In this study, we determined whether F. platypoda is a functionally androdioecious species. We analyzed its sex expression, seed development, pollen morphology and germination ability, and pollination systems. We found that inflorescences in hermaphrodite trees had hermaphrodite flowers and male flowers, but those in male trees had only male flowers. Pollen had the same morphology in hermaphrodite and male flowers. The pollen of hermaphrodite and male flowers was capable of germination, although the germination rate of pollen from male flowers tended to be higher than that of pollen from hermaphrodite flowers. The rates of self-pollination in bagged hermaphrodite flowers were close to zero. The rate of cross-pollination with male pollen was higher than that of natural pollination, and the rate of cross-pollination with hermaphrodite pollen was the same as that of natural pollination. These results show that F. platypoda is a functional androdioecious tree.