To easily check a locked or unlocked state by using a key at hand, and to provide such a key having a simple structure and general-purpose properties.

This key is equipped with a key body which has an insertion part to be inserted into a keyhole for the corresponding lock, so as to bring about the locked state, and a holding part which is attached to the key body so as to be turnable for locking/unlocking, in a state wherein the insertion part is inserted into the keyhole. The key body is attached so as to be turnable within a range of a predetermined angle with respect to the holding part; and an indication part for indicating the locked or unlocked state by the relative positional displacement of the key body and the holding part is provided.