From his childhood, he studied under Saicho, the founder of the Nihon (Japanese) Tendaishu sect, and in 838 went to Tang (China) bearing with him 50 questions on the doctrine of the Tendaishu sect raised by Tendai zasu (head priest of the Tendai sect), Encho.
幼い頃から日本天台宗の祖最澄に師事し、838年（承和(日本)5年）天台座主円澄の天台宗義に関する疑問50条を携えて唐に渡った。