Graduate of the famous Higashi Fukuoka High School, Kojiro led the school’s football team as its captain to participation in the Inter-high school Championships and National High School Championships.

After graduation, he signed his first contract with Fagiano Okayama in 2010. With some first experience gained little by little at Okayama, in 2014 he transferred to Roasso Kumamoto on loan in pursuit of more opportunities to play. At Roasso Kumamoto, he played as a regular. After this one-year rental period, he returned to Fagiano Okayama. From there, he supported the team as one of the key players.

In 2016, he also participated in the J1 promotion playoff finals.

He completely transferred to Avispa Fukuoka in 2018.

Shinohara made 83 league appearnces for Avispa Fukuoka after joining from Okayama in 2018. 

In 2021, He joined Matsumoto Yamaga FC to shores up the center of defense line. 

In addition to accurate covering and his strength and aggressiveness in 1-on-1 duels, he is also good at aerial battles.

Equipped with a sound technique, he is a center back that is furthermore able to supply his teammates with high-precision passes from the back of the pitch.

He commands the defense line and demonstrates leadership from there.

All in all an experienced and skillful player who can be placed in  any defensive position.