To provide a trailing arm installing structure to reduce the fore-and aft vibration transmitted from a road surface to a vehicle body by forming the locus of a rear wheel into an approximately linear motion of upward reversing and downward forwarding when the vehicle body bumps and rebounds and to enlarge a room space of a rear seat and mounting space of fuel tank.

In this trailing arm installing structure, a side of a trailing arm is connected to the rear wheel and the other side of the trailing arm is connected to the vehicle body via a conchoids curve forming means so that the rear wheel may figure an approximately linear locus of upward reversing and downward forwarding on bumping and rebounding of the vehicle body.