In an antitheft system for preventing an equipment comprising moving objects such as electric vehicles or operating machine such as lawnmower from theft, an electronic key is prepared to be carried by an operator of the equipment and stores authenticating data for identifying the operator who carries the electronic key. An authenticator is installed at the equipment and performs authentication check as to whether the electronic key is an authorized key using stored key-checking data, when the authenticating data is outputted from the electronic key, whereas an electronic key copier is provided separately from the equipment and copies the electronic key, thereby enabling to make a copy of the electronic key without activating equipment, while ensuring to prevent the equipment from theft.