There is a surplus of Kamen Riders in this show (and that's only based off of the three that I've seen: Den-O, Kabuto, and Kiva; there could be more).

L--> R
Takeda Kouhei (Kurenai Otoya; Kamen Rider Kiva)
Yamamoto Yuusuke (Kamishiro Tsurugi; Kamen Rider Kabuto)
Mizushima Hiro (Tendou Souji; Kamen Rider Kabuto)
Kato Keisuke (Nago Keisuke; Kamen Rider Kiva)
Seeing Mizushima Hiro act like a pervert was nigh mind-blowing, really.
Edit: Lol. I was just staring at the picture, and I noticed one of the guys looked familiar... thinking, "Hmm, he looks a bit like Sousuke from Go-Onger." So I investigated... yep. It's Furuhara Yasuhisa, alright....