A key system including a mechanical key and a lock apparatus into which the mechanical key is insertable. The mechanical key includes a key code pattern having recessed portions and non-recessed portions. The mechanical key is operated in key manipulation directions. The lock apparatus includes tumblers, each of which is associated with one of the recessed and non-recessed portions. The lock apparatus mechanically verifies the key code pattern when the mechanical key is inserted therein based on whether the tumblers are aligned with the associated recessed and non-recessed portions. The recessed and non-recessed portions in the key code pattern are deviated from the key manipulation directions.