To provide a coupling part structure for a joint member and an arm capable of reducing transmission of vibration into a car without impairing steering stability of an automobile.

This coupling part structure is for a joint member having a cylindrical enclosure part to enclose an elastic part of an elastic member, and an arm of sheet metal having a mounting hole provided with a holding part for holding the enclosure part of the joint member opened in a sheet part to be coupled with the joint member. A reinforcement ring is installed around the enclosure part of the joint member, and the reinforcement ring is brought into contact with the peripheral part of the mounting hole.