To provide a floor unit of a work machine which does not need to lift up a body to be supported by a crane and the like and which secures a stable working posture of a worker to enhance workability.

The floor unit of the work machine includes: aperture parts 38 which penetrate a floor plate 36 and through which vibration preventing bodies 40 can be inserted; and lid plates 47 blocking the aperture parts, being attached to the floor plate via a second attachment means 54 and connected to the vibration preventing bodies via a connecting means 58. First to third operation parts 52, 56 and 60 for operating attachment and connection or release by first and second attachment means and the connecting means are respectively provided on the first and the second attachment means and the connecting means and the first to third operation parts are formed toward an upper side of a vehicle body.