To display a locked/unlocked state on a key itself in a simple structure in response to a reversible key.

This locking/unlocking display key includes a space 21 formed in a key head 17, a pair of trigger rods 29 which are pressed by pressing means for projection on the front and rear sides of the key head 17, respectively, which come into contact with the peripheral part of a key hole to retreat, and which partition the space 21 into right and left sides at the projecting position and release the partitioning at the retreated positions, a pair of sliding partition plates 31 which are connected to the pair of trigger rods 29, respectively and which vertically partition the space 21 at the projecting positions of the trigger rods 29 and release the partitioning at the retreated positions, a spherical body 35 disposed in either of small four spaces 33 formed by partitioning the space by the pair of trigger rods 29 and the pair of sliding partition plates 31, and window parts 37 which are formed in the key head 17 so as to correspond to the small spaces 33, respectively, and through which the spherical body 35 can be visually confirmed.