  A warped extra dimension model proposed by Randall and Sundrum(RS) is one of
the attractive candidates to solve the gauge hierarchy problem in the Standard
Model. In a simplest version of the RS model, there are only two extra
particles beyond the Standard Model - a spin-2 graviton (and its Kaluza-Klein
excitations) and a radion which is a spin-0 and electrically neutral particle.
In this paper, we discuss a possibility of discovering the radion at a photon
collider, which has been considered as an option of $e^+ e^-$ liner collider
(ILC), focusing on characteristic features of radion interactions with photon
or gluon, in addition to constraints on mass and coupling of the radion from
the SM Higgs boson search at the LHC.
