Junson (November 28, 1585 – June 3, 1622) was a Buddhist priest and the 18th chief priest of Kosho-ji Temple. His imina (personal name) was Shogen. Junson was the child of Kenson, the 17th chief priest of Kosho-ji Temple and the grandchild of Kennyo, the 11th chief priest of Hongan-ji Temple. His mother was the daughter of Tamemasu REIZEN. His wife was the adopted daughter of Terumoto MORI (also the widow of Hideaki KOBAYAKAWA and her biological father was Motohide SHISHIDO, a senior vassal of the Mori clan). His childhood name was Yasomaru. His shigo (a posthumous name) was Futaiin. Junson's daughter Yaya (also known as Jukoin) married Yorifusa TOKUGAWA of the Mito clan, producing Yoritaka MATSUDAIRA (the first lord of the Hitachi Fuchu domain).
At age 10, Junson entered the Buddhist priesthood under Junnyo, the 12th chief priest of Hongan-ji Temple (and the founder of Nishi Hongan-ji Temple) who was also Junson's uncle and the husband of his older sister. In 1599, however, Junson became at odds with his older sister who inherited Kosho-ji Temple after the passing of their father, defecting to the Higashi Hongan-ji Temple side to which his uncle Kyonyo belonged. However, in 1607, Junson was persuaded to return to the Nishi Hongan-ji Temple side. During this time, Junson was promoted to the position of Hogen (the second highest rank in the hierarchy of Buddhist priests) in 1600, Daisozu (the highest grade that can be held by one who has reached the second highest rank in the hierarchy of Buddhist priests) in 1601, and finally Hoin (the highest rank in the hierarchy of Buddhist priests) in 1602.
In 1616, Junson was bestowed the position of Gonsojo (the lowest grade that can be held by one who has reached the highest rank in the hierarchy of Buddhist priests).