[1][2] He is the leader and main guitarist of Tokio, a musical group of Starto Entertainment formerly known as Johnny & Associates.

Prior to debuting with Tokio, Joshima was a backup-dancer for various Johnny's Entertainment boy bands at the time.

[3] He also formed temporary music units during that time, such as the Joshima Band with other to-be Tokio members.

One of his first roles ever was as a supporting cast member in the show Gomendou Kakemasu, where he acted alongside Kazuya Takahashi of Otokogumi and Naoto Endou of former Johnny's band Ninja.

[4] He has also hosted Ai no Apron and Leader's How-To Book, Brain Power Expedition Quiz!