To provide a key capable of disposing a key plate only by leaving a tongue plate even when improper cutting occurs.

A tongue plate 2 is mounted on a base end part 10 of a key plate 1 and is held by a coming off prevention member 3. The tongue plate 2 is provided with a key plate insertion hole 22 in which the base end part 10 of the key plate 1 can be inserted or removed and a pair of lock holes 24, 24 which cross this key plate insertion hole 22 orthogonally and pass through in the direction of thickness. In the coming off prevention member 3, a barrel part 30 supported on a surface on one side of the tongue plate 2 and a pair of leg parts 31, 31 inserted into each lock hole 24 are integrally formed. A pawl part 32 locked on a surface on the other side of the tongue plate 2 is formed at a tip of each leg part 31. A cutout part 11 with which each leg part 31 of the coming off prevention member 3 inserted into each lock hole 24 of the tongue plate 2 is formed in the base end part 10 of the key plate 1.