A design part installation structure for a vehicle, comprising: a design part exposed on a design surface of the vehicle; an outer plate panel including an installation section for installing the design part, the outer plate panel defining the design surface, wherein the outer plate panel is a plate-like steel member; and a parting line formed between the design part and the outer plate panel, wherein the parting line includes a curved line segment, wherein the outer plate panel comprises: an orthogonal flange portion disposed in a section corresponding to the curved line segment so as to extend from the installation section toward vehicle inside, the orthogonal flange portion being orthogonal to the design surface; and an inclined flange portion disposed in the section corresponding to the curved line segment so as to extend from an extending end of the orthogonal flange portion toward the vehicle cabin, wherein the inclined flange portion inclines toward the design part as a position thereon shifts in a direction from vehicle outside to vehicle inside, characterized in that the parting line includes: a first parting line segment; a second parting line segment extending in a direction crossing the first parting segment; and a third parting line segment formed between the first parting line segment and the second parting line segment so as to define the curved line segment, wherein the orthogonal flange portion is disposed in sections corresponding to the first parting line segment, the second parting line segment and the third parting line segment, wherein an angle (α1) of the inclined flange portion relative to the orthogonal flange portion becomes smaller as a position thereon shifts from a point of the outer plate panel corresponding to a top of the third parting line segment at a center in a longitudinal direction thereof, toward the first parting line segment and the second parting line segment. a design part exposed on a design surface of the vehicle; an outer plate panel including an installation section for installing the design part, the outer plate panel defining the design surface, wherein the outer plate panel is a plate-like steel member; and a parting line formed between the design part and the outer plate panel, wherein the parting line includes a curved line segment, wherein the outer plate panel comprises: an orthogonal flange portion disposed in a section corresponding to the curved line segment so as to extend from the installation section toward vehicle inside, the orthogonal flange portion being orthogonal to the design surface; and an inclined flange portion disposed in the section corresponding to the curved line segment so as to extend from an extending end of the orthogonal flange portion toward the vehicle cabin, wherein the inclined flange portion inclines toward the design part as a position thereon shifts in a direction from vehicle outside to vehicle inside, an orthogonal flange portion disposed in a section corresponding to the curved line segment so as to extend from the installation section toward vehicle inside, the orthogonal flange portion being orthogonal to the design surface; and an inclined flange portion disposed in the section corresponding to the curved line segment so as to extend from an extending end of the orthogonal flange portion toward the vehicle cabin, wherein the inclined flange portion inclines toward the design part as a position thereon shifts in a direction from vehicle outside to vehicle inside, characterized in that the parting line includes: a first parting line segment; a second parting line segment extending in a direction crossing the first parting segment; and a third parting line segment formed between the first parting line segment and the second parting line segment so as to define the curved line segment, wherein the orthogonal flange portion is disposed in sections corresponding to the first parting line segment, the second parting line segment and the third parting line segment, wherein an angle (α1) of the inclined flange portion relative to the orthogonal flange portion becomes smaller as a position thereon shifts from a point of the outer plate panel corresponding to a top of the third parting line segment at a center in a longitudinal direction thereof, toward the first parting line segment and the second parting line segment. a first parting line segment; a second parting line segment extending in a direction crossing the first parting segment; and a third parting line segment formed between the first parting line segment and the second parting line segment so as to define the curved line segment, wherein the orthogonal flange portion is disposed in sections corresponding to the first parting line segment, the second parting line segment and the third parting line segment, wherein an angle (α1) of the inclined flange portion relative to the orthogonal flange portion becomes smaller as a position thereon shifts from a point of the outer plate panel corresponding to a top of the third parting line segment at a center in a longitudinal direction thereof, toward the first parting line segment and the second parting line segment.