A headrest moving mechanism (10) includes linking members (12, 12) that links a support portion (4A) and a headrest base portion (4C) to each other; and elongated holes (11H, 11H) formed in the headrest base portion (4C). The elongated holes (11H, 11H) slidably receive a connection shaft (13A) provided to the support portion (4A), thereby determining a postural position of the support portion (4A). The elongated holes (11H, 11H) are shaped so as to move the support portion (4A) forwardly and upwardly with respect to the headrest base portion (4C) from an initial position in a time before the vehicle back-side collision happens to a collision preparatory position as the linking members (12, 12) are rotated.