An operator’s room situated in a region above the power train of a work machine which has an opening for maintenance purposes formed passing through a floor frame and a lid member for closing off the opening installed on the floor frame, and which achieves both good quietness characteristics and good workability during servicing. The slurry is produced by rendering the surface of the particulate hydrophobic during or prior to making the slurry. A buffer layer precursor contains the inorganic powder and an organic material, and the organic material is vaporized from the buffer layer precursor to obtain the buffer layer. The copolymers are made to self-organize, with the guides guiding the self-organization and with each block aggregating with other blocks of the same type, thereby forming the seed layer. The cleaning component can include various different materials to target primary removal of a particular foreign material. The needle rollers are prevented from coming out by an inward flange provided at one end of the outer shell and an outward flange provided at the other end of the inner shell, and an inwardly bent edge provided at the other end of the outer shell is superimposed on the outside of the outward flange of the inner shell to establish axial engagement between the outer shell and the inner shell.