To provide an automatic electric circuit disconnecting switch which is able to reduce the standby power consumption of an electrical appliance connected to commercial power supply, when the appliance is not used by automatically disconnecting the electrical circuit from the commercial power supply.

An automatic electric circuit disconnecting switch is constituted of a conductive plate 6, which is brought into contact with and separated from the electric circuit 8 of a plug socket for commercial power supply and a bias spring 5 which urges the conductive plate 6 in the direction, in which the plate 6 is brought into contact with or separated from the electric circuit 8. The plate 6 and spring 5 are made of shape memory alloys, so that the plate 6 may be displaced to continuously connected the circuit 8 to an electrical appliance, while the appliance is being used and disconnect the circuit 8 from the appliance while the appliance is not being used.