Abstract: Apparatus for harmonic oscillation analysis includes a detector for taking up, as electric oscillation, mechanical vibration generated during the operation of a rotary machine system, a comb filter for extracting from the detector's output signal having a composite periodic oscillation wave form only fundamental wave component of a determined fundamental frequency fo and its harmonic wave component, and a clock pulse generator for generating clock pulses to drive the comb filter by the clock pulse having the fundamental frequency fo and a discriminator for evaluating abnormality of the rotary machine system depending upon the particular signal components extracted through the comb filter.