A center pillar's upper part trim includes a slider and a knob. The slider has a boss projecting in the back side direction. The knob has a flexible member extending in a cantilever manner in a first direction being one operation direction and other end opposed to the flexible member on the first direction side of the flexible member. The center pillar's upper part trim further includes: a slide-and-join structure allowing the knob to slide and join to a plurality of engaging catches from a state where the flexible member of the knob is placed on the boss; and a restriction structure restricting the knob, in a state where the knob has slid and joined, from excessively shifting in the first direction and the second direction by setting the boss between the flexible member and the other end when the knob is operated to slide.