We build an equivalent Simulation Program with Integrated Circuit Emphasis (SPICE) model for a vibrational energy harvester comprising comb electrodes coated with an electret film that is used to convert the vibrational kinetic energy into electrical output power by electrostatic induction. In the assembled module, sinusoidal and nonsinusoidal vibrations are imported into the nonlinear current sources as an inertial force, and the power-generating performances are simulated. The nonsinusoidal waves observed in an actual environment (highway duct) are used as an input sample. By quantitatively comparing the simulation and experimental results, we verify the applicability of the equivalent module for various vibrations. When the device is excited by sinusoidal vibration, the maximum output power is calculated to be 71 µW at 0.044 G (1 G = 9.8 m/s2), which is close to the experimental result of the actual device, 68 µW at 0.045 G. Furthermore, when importing a nonsinusoidal vibration, the two timings at the highest generating peak are obtained in accordance with the moment of resonance, and the amplitudes are experimentally and analytically obtained to be 0.80 and 0.63 V, respectively.