Low relative humidity and the use of microelectronic devices cause electronic apparatuses to malfunction. The malfunction is caused by an electrostatically induced voltage generated in a partly opened metal box within the apparatus. For example，
when a charged body moves in front of a metal box，an induced voltage is generated in the conductors contained in the metal box. Under normal conditions，ungrounded metal boxes are used. The induced voltage generated in an ungrounded metal box is
never cleared when a charged body moves near the metal box. In this study，the induced voltage generated in the ungrounded metal box is cleared. The result shows that an induced voltage of 3 kV is generated in the ungrounded metal box when a charged body of 10 kV moves near the metal box. The results will be useful for designing an apparatus which will not malfunction.