PURPOSE: To provide the device enabling to again charge by a simple means, when the surface charge density of a cap, etc., produced from an electret fiber sheet is lowered.
CONSTITUTION: The device has a heating chamber 3 whose bottom surface is opened, a far IR light heater 4 disposed in the heating chamber 3, plural discharging electrodes disposed in the heating chamber, and a body 1 having an earth 2, the body 1 being reciprocatively movably disposed in order to suitably insert the body having an electret fiber product loaded along its surface shape into the heating chamber. A means is adopted in which the heating chamber can reciprocatively moved in order to suitably insert the body having the electret fiber product loaded thereon into the heating chamber and in which a part of the main body of the device provided with the heating chamber and the body is connected through a hinge member. Further, a means is also selectively adopted in which the upper part of the cylinder of the body is semi- spherical.