A vehicle attachment component comprising: an attachment portion provided on a first side and characterized in that: the attachment portion is configured to be attached to a predetermined longitudinal member, wherein the longitudinal member is a tubular member; and a predetermined function portion provided on a second side opposite to the first side, wherein the attachment portion includes: a detachment preventing engagement portion configured to be inserted into an attachment hole provided in the longitudinal member and thereby engaged with the longitudinal member from a deep side in an insertion direction thereof, to come into a detachment-prevented state; and elastic pressing portions having: base end portions protruding from a base end side in the insertion direction of the detachment preventing engagement portion toward both sides in a direction perpendicular to both the insertion direction and a longitudinal direction of the longitudinal member in the detachment-prevented state, wherein the base end portions extend in an inclined manner so as to approach the longitudinal member; and distal end portions bent at ends of the base end portions toward the deep side in the insertion direction and extending in an inclined manner so as to further approach the longitudinal member, the distal end portions being configured to always elastically press an outer surface of the longitudinal member, the base end portions being thicker than the distal end portions; wherein the elastic pressing portions are formed as an elastic piece having a rectangular plate shape and having a predetermined width in the longitudinal direction with respect to the longitudinal member in a detachment-prevented state; and the elastic pressing portions are configured such that, in the detachment-prevented state, the base end portions are not in contact with the longitudinal member and the distal end portions elastically press the longitudinal member, and when each elastic pressing portion is subjected to a further pressing force from the longitudinal member, the base end portion which has been in a non-contact state comes into contact with the longitudinal member. the attachment portion is configured to be attached to a predetermined longitudinal member, wherein the longitudinal member is a tubular member; and a predetermined function portion provided on a second side opposite to the first side, wherein the attachment portion includes: a detachment preventing engagement portion configured to be inserted into an attachment hole provided in the longitudinal member and thereby engaged with the longitudinal member from a deep side in an insertion direction thereof, to come into a detachment-prevented state; and elastic pressing portions having: base end portions protruding from a base end side in the insertion direction of the detachment preventing engagement portion toward both sides in a direction perpendicular to both the insertion direction and a longitudinal direction of the longitudinal member in the detachment-prevented state, wherein the base end portions extend in an inclined manner so as to approach the longitudinal member; and distal end portions bent at ends of the base end portions toward the deep side in the insertion direction and extending in an inclined manner so as to further approach the longitudinal member, the distal end portions being configured to always elastically press an outer surface of the longitudinal member, the base end portions being thicker than the distal end portions; wherein a detachment preventing engagement portion configured to be inserted into an attachment hole provided in the longitudinal member and thereby engaged with the longitudinal member from a deep side in an insertion direction thereof, to come into a detachment-prevented state; and elastic pressing portions having: base end portions protruding from a base end side in the insertion direction of the detachment preventing engagement portion toward both sides in a direction perpendicular to both the insertion direction and a longitudinal direction of the longitudinal member in the detachment-prevented state, wherein the base end portions extend in an inclined manner so as to approach the longitudinal member; and distal end portions bent at ends of the base end portions toward the deep side in the insertion direction and extending in an inclined manner so as to further approach the longitudinal member, the distal end portions being configured to always elastically press an outer surface of the longitudinal member, the base end portions being thicker than the distal end portions; wherein the elastic pressing portions are formed as an elastic piece having a rectangular plate shape and having a predetermined width in the longitudinal direction with respect to the longitudinal member in a detachment-prevented state; and the elastic pressing portions are configured such that, in the detachment-prevented state, the base end portions are not in contact with the longitudinal member and the distal end portions elastically press the longitudinal member, and when each elastic pressing portion is subjected to a further pressing force from the longitudinal member, the base end portion which has been in a non-contact state comes into contact with the longitudinal member.