To obtain authentication to be a delivery certificate irrespective of whether a receiver is at home or absent by acquiring specific information about each house.

Loads such as lighting fixtures 6a, 6b, a refrigerator 8, a television set 9 and a personal computer 10 are connected with a power line 1 of the house via a plurality of safety breakers 5a to 5n, each house has specific wiring topology. Consequently, an authentication data measuring instrument 11 can fetch electrical characteristics such as reflection power characteristics, impedance characteristics and noise characteristics which are unique by each house. The house is authenticated by using the electrical characteristics for authentication data. A deliveryman can acquire simplified authentication data from a simplified authentication data reading/writing part 13b and can acquire detailed authentication data from a detailed authentication data reading/writing part 13a. Simplified authentication and detailed authentication with high security can be executed by collating pieces of the authentication data with stored information of a memory 12 later.