It is well known that the intrinsic photoconduction in an anthracene crystal changes exponentially with temperature. In order to study the generation mechanism of free carriers in an anthracene crystal, a pulsed photoconduction measurement has been performed. The thermal activation energy for the intrinsic photoconduction has been found to depend on the excitation wavelength. The activation energy is constant for the wavelength range shorter than the fundamental absorption edge, however, for the longer wavelength region, it increases linearly as the wavelength increases. In the fundamental absorption region, a constant value of 0.14eV is obtained as the activation energy both for holes and electrons. The activation energy is independent of the crystal orientation. The temperature and crystal orientation dependences of the drift mobility are discussed. Excepting the case of electron in the direction perpendicular to (ab)-plane, the drift mobilities decrease as the temperature rises. A model of energy levels is proposed for the charge carrier generation.