A headrest mechanism includes a headrest stay, a headrest support, an engagement member, a plurality of adjustment portions, and a pullout prevention portion. The height of a headrest may be adjusted by pushing the button portion of the headrest support to disengage the engagement member provided in the headrest support from an adjustment portions provided on the side surface of a headrest stay. The headrest, including the headrest stay, may be removed by turning a lock portion of the headrest support by 90 degrees, pushing the button portion and pulling up the headrest. Thus, the headrest can be removed without using any additional tools.