PURPOSE: To improved stability of a vehicle attitude during running by providing a rotation increase system with a cross bar formed integrally with a second main part and two slide arms, and connecting each slide arm to the end part of the cross bar located far from a corresponding vertical rod.

CONSTITUTION: In a three-wheel vehicle wherein a secondary part II is suspended from the chassis 30 of a primary part 1 supporting three wheels by bearings, a mast 4 is arranged at the rear part of the chassis 30 and supported on rear two wheels 1a and 1b through a parallel link mechanism. The parallel link mechanism has vertical rods 3a and 3b on both sides paralleling each other and two equalizers 2a and 2b are pivotally mounted on both ends of each of the rods 3a and 3b. An rotation increase system having a cross bar 8 is provided, slide arms 11a and 11b are arranged in an extending state at a cross bar 8 and on both sides of the central surface of the secondary part II. A roller 9a on the cross bar 8 is rotatably contained in a guide 14a formed at each of the slide arms 11a and 11b.