Crazy Ken Band (クレイジーケンバンド), also referred to as CKB, is a Japanese musical group formed in 1997 by its lead vocalist, writer and composer Ken Yokoyama. The band first came together in 1991 under the name "CK's", with a four-member lineup: Ken Yokoyama, Keiichi Hiroishi, Masao Onose and Shinya Horaguchi. This incarnation of the group was centred on a 15-man instrumental and vocal group. In 1997, Keiichi Nakanishi became the fifth member and the group's name was changed to "Crazy Ken Band".