A femtosecond regular reflection spectroscopic system was developed and applied to a β-copper phthalocyanine (β-CuPc) pellet. Transient regular reflection spectra were converted into extinction coefficient change (Δk) ones, which correspond to transient absorption spectra, by using Kramers- Kronig transformation. The Δk spectrum observed immediately after excitation was assigned to the excited state of β-CuPc solid, which relaxed by an exciton-exciton annihilation. The spectra remaining over several nanoseconds were assigned to a hot band due to a vibrationally excited state of the electronically ground state. We have clarified that a fast photothermal conversion process is induced by the exciton-exciton annihilation, which was analyzed by a simulation using a time dependent rate (proportional to t(- 1/2)) of the annihilation.