PURPOSE: To realize an electric shock preventer for preventing electric shock due to erroneous connection between an electric equipment and a three-line power supply containing an earth line.

CONSTITUTION: Terminals 6, 7, other than an earth terminal 8, out of three output terminals 6-8, including the earth terminal 8, of an electric shock preventer 1 are connected with input terminals 9, 10, other than an earth terminal 11, of an equipment 12 and only when a closed loop is formed including a DC power supply E1, switches 1a, 1b, 2a, 2b disposed between an AC power supply and the equipment 12 are turned ON. Consequently, a current is fed from the AC power supply through the electric shock preventer 1 to the equipment 12. According to the constitution, current is not fed to the equipment 12 even upon erroneous connection of the output terminal 6 or 7, other than the earth terminal 8, with the earth terminal 11 of the equipment 12, resulting in positive prevention of electric shock.