A laser-Compton-scattered (LCS) photon beam was used as the source of quasimonoenergetic photons in the energy range from 2 to 22 MeV. Second-harmonic light (527 nm) from a Nd:YLF laser was guided into the interaction region in a electron storage ring, TERAS (800 MeV, 300 mA). High energy photons back-scattered by relativistic electrons were collimated by a lead collimator with a reentrant hole 2 mm in diameter. The photon fluence was measured by a large coaxial Ge detector. To determine the energy distribution of a photon beam and the response function of a Ge detector, the EGS4/PRESTA-CG code was used taking into account the precise overall computational model. Results showed that, at a photon energy of 5.965 MeV, the calculated pulse height spectra agreed very well with experimental data.