To provide a key structure having no risk of loss and dropout a chip and without need for separately having a conversion key.

A key structure comprises: a key 11 in which a groove 35 is formed on at least one of the front and rear surfaces of a key body 15; a holding part 17 which is connected to a key base end 21 of the key body 15 and which protrudes outward beyond a keyhole when the key is operated; a shank 43 which is accommodated in the groove 35 of one surface 37 and of which shank base end 49 is arranged in the holding part 17; and a protrusion 45 which is formed by bending a shank tip 51 of the shank 43 and protrudes beyond a key tip 41 of the key body 15 by attaching the shank 43 to the groove 35. The protrusion 45 is formed in a hook shape, and a hook tip 53 is preferably locked to the groove 35 of the other surface. A fitting 47 is provided in the shank base end 49 and is preferably detachable to the holding part 17.