To provide a hollow structure of a work machine capable of preventing the reduction of noise reducing effect by a small amount of damping material.

This hollow structure of the work machine having a hollow cross section is constituted such that the damping material 19 is filled into a central part region 15 including a substantially central part in the longitudinal direction and having a predetermined length L2, and the central part region 15 is partitioned by partition plates 9, 10.