A card key includes a circuit board and a plate-shaped key body. The circuit board is mounted with electronic parts that configure an electronic circuit for performing radio communication with an on-vehicle device. The key body is mounted with the circuit board which is covered with a resin material. The key body has a principal front surface on the side of which the electronic parts are mounted, and has a main body recess sunk to a predetermined depth level from the principal front surface and a key component accommodating recess further sunk to a level deeper than the main body recess and opened in a bottom surface of the main body recess. The key body forms an outline of the card key together with a sheet body fitted to the main body recess. The key component accommodating portion is formed between the sheet body and the key component accommodating recess.