A plurality of pressing portions 38 protrude inward in a radial direction from an inner peripheral surface of a tubular main body portion 35 (part of a tube body) and are each fixed at both ends thereof in an up-down direction to the main body portion 35. Since the plurality of pressing portions 38 are aligned in the up-down direction, a stay 22 or 23 can be inhibited from oscillating with a contact portion between one pressing portion 38 and the stay 22 or 23 as a fulcrum. As a result, rattling of the stay 22 or 23 relative to a headrest holder 30 or 31 can be suppressed.