To obtain an earth leakage preventing device effective, low-cost and small-sized by generating a voltage waveform and a negative phase waveform generated in a housing connected via an earth by a micro computer and canceling them in an equipment having an isoelectric points grounding type noise terminal voltage countermeasure filter.

A noise to a commercial power source 3 is removed from the equipment by the noise terminal voltage countermeasure filter 2, and electric power is supplied to a load 4. Here, in a negative phase voltage generating part 1, the power of the power source 3 is inputted to a potential-divide/level- shift circuit, the voltage waveform potential-divided and level-shifted is computed in real time by the microprocessor, and negative phase voltage is generated, and then it is amplified and outputted between the isoelectric point of the isoelecric point grounding capacitor of the noise terminal voltage countermeasure filter 2, and the earth 6. Thus, the same waveform voltage having the negative phase is supplied to the voltage waveform generated in the housing 5 via the earth 6 to cancel them, and leakage current is accurately removed even responding to the fluctuation of supply voltage.