To provide a locked-state indication mechanism for a folding seat permitting easy confirmation of the locked state of its seat cushion on its seat back for improving its safety.

Synchronizing with the locking or unlocking of a seat cushion 2 with respect to a seat back 3 by a lock mechanism part employing a hook and a ratchet, a coupling body 6 slides a lock-information indication body 5 to selectively display a blue locked-state indication part 5a or a red unlocked- state indication part 5b attached on the lock-information indication body 5 in an observation window 4. The observation of the blue locked-state indication part 5a from the outside definitely confirms that a folding seat 1 is locked to thereby improve the safety thereof.