A connection structure or a fastening structure including a circuit which functions as a resonant circuit whose connection or fastening is confirmed by resonance of radio waves, the connection structure or a fastening structure has a connector for connecting a member to be connected or a clip for fastening a member to be fastened; a first circuit having first contacts on respective ends thereof; and a closed circuit functioning as a resonance circuit supported on the retainer or clip when in contact with the first contacts. Alternatively, the connection structure of fastening structure has a second circuit which disables a function of a resonance circuit upon contacting the first contact, and the first contacts and the second circuit are brought into contact simultaneously with connection of the connector or fastening of the clip.