To effectively reduce the vibration generated on a cargo bed of a truck.

In a vibration-isolating structure of a cargo bed of a truck, a cargo bed 4 is provided behind a cab 3, and a cargo bed floor part 4a is installed on an undercarriage base part 2 on a cargo bed space side. A front side of the cargo bed floor part 4a is mounted on the undercarriage base part 2 by a hinge 5 turnably only in the pitching direction, and a rear side of the cargo bed floor part 4a is elastically mounted on the undercarriage base part 2 by an air spring 6. By the turnable mounting of the front side of the cargo bed floor part and the elastic mounting on the rear side of the cargo bed, the vibration of the cargo bed is permitted in the pitching direction, and at the same time, the vibration of the cargo bed in the pitching mode is efficiently insulated while the pitching resonance frequency is the low frequency capable of obtaining the vibration-isolating effect. By the turnably mounting of the front side of the cargo bed, the cargo bed is mechanically restricted, and the posture of the cargo bed is stabilized.