Not only natural frequency but also vibration level around the peak frequency should be calculate when the vibrational performances of the structure, which is excited by dynamic forces, are estimated. If one of the vibration levels around peak frequencies violates the permissible limit, the structure must be redesign to satisfy the permissible limit. Therefore it is useful and important for designer to obtain the sensitivity distributions for the vibration levels around the peak frequencies, because he can know how to efficiently modify the structure. In this paper, to obtain previous sensitivities, the word of 'Peak Level' is defineded as the vibration level at the natural frequency and the sensitivity of the peak level is formulated. Then the sensitivity of vibration level around peak frequency is formulated with considering angular frequency around peak as the function of the design variables. Besides the validity of these formulations is verified by comparing the accurate solutions of the simple mass-spring model.