PURPOSE: To obtain a small-sized vibration detector detecting vibration applied to the case sufficiently and to improve the sensitivity by opposing a fixed electrode to a movable electrode and by fitting a weight at least to one side of the movable electrode to increase the actual mass.

CONSTITUTION: The weight 6a is fitted at least to one side of the movable electrode 6 obtained by treating a metallic foil or a polyester film by metal evaporation or the like to increase the mass of the movable electrode 6 actually. If the vibration is applied to the case 4, the movable electorde 6 is oscillated, the change of capacity is generated between the movable electrode 6 and the fixed electrode 9 and the change is applied to an FET11 as an electric signal. If it is defined that the charge of an electrolet 10 is Q and the capacity between the movable electrode 6 and the fixed electrode 9 is C, the voltage V applied to the FET11 is V=Q/C. The source 11c of the FET11 is connected to the case 4 through an earth pattern 12a of a printed circuit board 12 and earthed. The electrode 6 is sharply vibrated by the weight 6a adhered to the electrode 6 in accordance with the external vibration and outputs a high output voltage.