An interlocking adapter comprising: a current path provided to supply a load current based on an alternating-current voltage received from an electric outlet to be coupled to the interlocking adapter provided in an electric apparatus to be attached with the interlocking adapter; a resistive load provided in the current path; a switch provided in the current path and configured to be turned on and off, the current path being completed in response to the switch being turned on, the current path being interrupted in response to the switch being turned off; a zero-cross detector for detecting a zero-cross point of the alternating-current voltage and a controller configured to turn on and off the switch in synchronization with a change of the alternating-current voltage in response to reception of an interlocking command signal to be wirelessly received by the interlocking adapter from a working machine to be connected to the interlocking adapter so as to supply the load current from the electric outlet to the resistive load, the controller being configured to (i) turn on the switch only for a certain period after the zero-cross point every 1/2 cycle of the alternating-current voltage in case that the electric apparatus is configured to determine whether to start interlocking operation with the working machine based on the load current supplied after the zero-cross point of the alternating-current voltage and (ii) turn on the switch only for a certain period before the zero-cross point every 1/2 cycle of the alternating-current voltage in case that the electric apparatus is configured to determine whether to start the interlocking operation with the working machine based on the load current supplied before the zero-cross point of the alternating-current voltage. a current path provided to supply a load current based on an alternating-current voltage received from an electric outlet to be coupled to the interlocking adapter provided in an electric apparatus to be attached with the interlocking adapter; a resistive load provided in the current path; a switch provided in the current path and configured to be turned on and off, the current path being completed in response to the switch being turned on, the current path being interrupted in response to the switch being turned off; a zero-cross detector for detecting a zero-cross point of the alternating-current voltage and a controller configured to turn on and off the switch in synchronization with a change of the alternating-current voltage in response to reception of an interlocking command signal to be wirelessly received by the interlocking adapter from a working machine to be connected to the interlocking adapter so as to supply the load current from the electric outlet to the resistive load, the controller being configured to (i) turn on the switch only for a certain period after the zero-cross point every 1/2 cycle of the alternating-current voltage in case that the electric apparatus is configured to determine whether to start interlocking operation with the working machine based on the load current supplied after the zero-cross point of the alternating-current voltage and (ii) turn on the switch only for a certain period before the zero-cross point every 1/2 cycle of the alternating-current voltage in case that the electric apparatus is configured to determine whether to start the interlocking operation with the working machine based on the load current supplied before the zero-cross point of the alternating-current voltage.