NOVELTY - The system (S) has a contact pick-up apparatus (3) attached to a housing of an inverter (I) and converting housing vibration into an electric signal. An amplifier apparatus (5) amplifies the output electric signal. An alarm generator (2) outputs sound to surroundings of a vehicle (C) based on the electric signal output from the amplifier apparatus. A control unit i.e. CPU, controls operation of the amplifier apparatus based on change of frequency of an electric signal output from the pick-up apparatus. An alarm generation unit is attached to a body structural part (9).    USE - Presence alerting system for a vehicle e.g. hybrid vehicle, electric vehicle and fuel cell electric vehicle (all claimed).    ADVANTAGE - The housing vibration of an inverter is caught with the pick-up apparatus and converted into the electric signal such that the electric signal is amplified with the amplifier apparatus so as to emit vibration sound when an approach of a vehicle can be comfortably made known with respect to the surrounding pedestrian with the inverter sound that the vehicle originally emits, thus eliminating need to provide a regeneration unit that stores/reproduces simulation sound data without modulating special sound frequency and installing a retrofit in an easy manner. The system allows the inverter sound and sound of a vehicle original such that change is not sensed before and after muffling, thus allowing an in-vehicle driver and a fellow passenger to avoid problem that comfort falls being conscious of vehicle speed. The control unit controls operation of the amplifier apparatus based on change of the frequency of the electric signal output from the pick-up apparatus so as to carry out operation without controlling an amount of amplification or stopping an amplifier output above predetermined frequency based on frequency of the inverter vibration, which becomes high with decrease of speed of the vehicle. The control unit controls to stop the output of the amplifier apparatus when a predetermined value is exceeded to perform control that muffles the sound easily when the predetermined value is more than fixed level. The sound is emitted to the surroundings of the vehicle by using the diaphragm to which an oscillator is attached when the oscillator outputs mechanical vibration, so that alarm countermeasure is avoided and attachment location cannot be chosen, thus reducing cost of the system.    DETAILED DESCRIPTION - The contact pick-up apparatus is a bone conduction pick-up microphone. The body structural part functions as a diaphragm.    DESCRIPTION OF DRAWING(S) - The drawing shows a perspective view of a vehicle furnished with a presence alerting system.    Vehicle (C)    Inverter (I)    Presence alerting system (S)    Alarm generator (2)    Contact pick-up apparatus (3)    Amplifier apparatus (5)    Body structural part (9)