A significant wavelength dependence of the excitation light was observed in the magnetic field effects (MFE) on the photocarrier generation of a benzene-1,2,4,5-tetracarbonitrile-doped poly(N-vinylcarbazole) film. The excitation of the carbazole induces positive MFEs, indicating an enhancement of the photoconductivity originating from the charge separation through the triplet exciton. In contrast, a singlet spin state governs the photocarrier generation in the case of the charge transfer band excitation, because negative MFEs are induced.