An automotive seat headrest supporting apparatus includes headrest supporting members and stay locking units 20 which are incorporated into the headrest supporting members 10 to lock stays 4. The headrest supporting member 10 has a stay guiding hole 13 into which the stay 4 is inserted and an incorporating recess 14 which is opened to an outer surface and which communicates with the stay guiding hole 13 within the headrest supporting member 10 from a direction intersecting the stay guiding hole 13. The stay locking unit 20 includes a stay lock body 30 which is slidably fitted in the incorporating recess 14, a locking bar 21 which is incorporated into the stay lock body 30 and a coil spring 22 which biases the stay lock body 30 in a direction in which the locking bar 21 is brought into engagement with a locking portion 4a of the stay 4. The stay lock body 30 is configured so that, after the locking bar 21 is accommodated and disposed in accommodation grooves 36, a locking bar holding member 41 is set to hold the locking bar 21 within the accommodation grooves 36.