A concept of RF catalyst by use of ion cyclotron wave is presented. The ICRF wave is excited by the external antenna, amplified by the beam particles and absorbed by the bulk plasma. The circulating power in the plasma is much larger than the wave energy which is radiated from the antenna: the injected wave works as catalyst to stimulate the energy flow from beam particles to the bulk plasma. Solving the kinetic wave equation in a model Tokamak geometry, the amplification factor is calculated, and the applicable plasma parameters in present experiments are discussed.