To provide a screed adjusting mechanism of a road paving machine capable of improving pavement quality, and shortening an adjusting time, saving labor, and reducing the number of workers by smoothly adjusting the crown amount.

An actuator 16 is connected to span variable means 12A, 12B for varying the upper side interval between left and right screeds 4A, 4A and a length variable means 9a for varying the length of a center support 6A through power transmission means, respectively. The adjustment of the crown amount and the adjustment of the length of the center support are simultaneously performed by the drive force of the actuator 16.