筑前国
Kaibara was born into a family of advisors to the "daimyō" of Fukuoka Domain in Chikuzen Province (modern-day Fukuoka Prefecture). He accompanied his father to Edo in 1648, and was sent in 1649 to Nagasaki to study Western science. At his father's urging, he continued his studies in Nagasaki as a rōnin from 1650 through 1656. He then re-entered service to Kuroda, which led to his continuing studies in Kyoto. After his father's death in 1665, he returned to Fukuoka.