We theoretically study pump and probe spectra of a quantum dot (QD) embedded in a microcavity in the cavity QED treatment. Energy levels of a QD are modeled by a four-level system consisting of the ground state, right and left-polarized excitons, and a biexciton. As a cavity-QED effect, four spectral peaks appear when the pump field frequency is tuned to the lower or upper level constituting the vacuum-field Rabi splitting. In addition, the spectral intensity dramatically enhances due to the cavity effect. The enhancement rate is independent of the coupling energy between exciton and cavity photons when the well-defined vacuum-field Rabi splitting is formed.