The Short Version
The claim overstates how the 1940 law operated in practice. Japan’s National Eugenics Law did place doctors and prefectural bodies at the center of review and authorization, and it allowed compulsory sterilization on paper. But the best legislative and academic sources indicate that the compulsory provision was not actually implemented and that recorded surgeries under the 1940 law proceeded through consent-based channels, so officials were not often making the decision instead of the individual.