Locking/unlocking mechanism for headrest

In combination with a seat back frame of an automotive seat and a headrest having a headrest stay formed with a stopper notch, said headrest being mounted via a headrest holder upon said seat back frame, said headrest holder having a through-bore in which said headrest stay is slidably inserted,

• a locking/unlocking mechanism provided in said headrest holder, comprising:
• a lock element which is so provided in the headrest holder as to be movable toward and away from said through-bore, said lock element including an engagement means and a hole;
• wherein said lock element is movable between a locking position where said engagement means of the lock element is to be engaged with said stopper notch, and an unlocking position where said engagement means of the lock element is to be disengaged from said stopper notch;
• a biasing means for resiliently biasing said lock element in a direction to said locking position, said biasing means being provide between said lock element and said headrest holder;
• and
• an unlocking hole formed in said headrest holder in such a manner as to allow an unlocking tool to be inserted therethrough and engaged with said hole of the lock element so as to retain said lock element in said unlocking position.