An electret type vibration detection system comprising: a vibration-powered generator adapted to perform vibration-induced power generation by displacing, on the basis of external vibration, an electret group formed of a plurality of electrets and an electrode group having a plurality of electrode pairs (6, 7) in a relative movement direction to output a vibration-induced voltage between electrodes of the electrode pair (6, 7); a transfer function memory section adapted to store transfer function information that defines a correlation between a vibration velocity of the external vibration and an output power voltage of the vibration-powered generator in a range of a predetermined frequency included in the external vibration, the transfer function information containing a transfer coefficient set according to each of a plurality of frequencies belonging to the predetermined frequency range to place the vibration velocity of the external vibration and the output power voltage of the vibration-powered generator in a predetermined proportional relationship; an output spectrum information computing section adapted to perform a Fourier transform on information relating to a transition of the output power voltage of the vibration-powered generator within a predetermined time period to compute output spectrum information relating to the output power voltage; and a vibration velocity information creating section adapted to create a vibration velocity information relating to the external vibration in the predetermined time period, based on the output spectrum information relating to the output power voltage of the vibration-powered generator computed by the output spectrum information computing section and the transfer function information stored in the transfer function memory section. a vibration-powered generator adapted to perform vibration-induced power generation by displacing, on the basis of external vibration, an electret group formed of a plurality of electrets and an electrode group having a plurality of electrode pairs (6, 7) in a relative movement direction to output a vibration-induced voltage between electrodes of the electrode pair (6, 7); a transfer function memory section adapted to store transfer function information that defines a correlation between a vibration velocity of the external vibration and an output power voltage of the vibration-powered generator in a range of a predetermined frequency included in the external vibration, the transfer function information containing a transfer coefficient set according to each of a plurality of frequencies belonging to the predetermined frequency range to place the vibration velocity of the external vibration and the output power voltage of the vibration-powered generator in a predetermined proportional relationship; an output spectrum information computing section adapted to perform a Fourier transform on information relating to a transition of the output power voltage of the vibration-powered generator within a predetermined time period to compute output spectrum information relating to the output power voltage; and a vibration velocity information creating section adapted to create a vibration velocity information relating to the external vibration in the predetermined time period, based on the output spectrum information relating to the output power voltage of the vibration-powered generator computed by the output spectrum information computing section and the transfer function information stored in the transfer function memory section.