In view of the situation that the linear harmonic oscillator is subjected to the simple harmonic force with the frequency fluctuation, we work out the expression of the first-order moment for the system response. It is found that the system output response vibrates at the natural frequency, that the response amplitude shows bona-fide stochastic resonance as the simple harmonic excitation force frequency varies, and that the suppression and the resonance appears as the natural frequency varies.