To maintain roller compression force within a sliding gap and dampening water thin film constant by providing a rotational shaft supporting a first roller being in contact with a second roller in a swing manner on a straight line in parallel with a tangential line passing through the central axial line of the first roller and extending through the slippage interstice.

Liquid shearing forces Fs.6.7 acts along a tangential lines (t)6.7 of rollers 6, 7 at a sliding roller gap N6.7 in the rollers 6, 7. The rotational shaft 14 of a support member is disposed on a line L passing through the central axis of the roller 6, and being in parallel with the tangential lines (t)6.7, and further extending to the action line K6.7 of the force. Thus, shearing force Fs.6.7 is prevented from giving an angular moment for permitting the roller 6 to move toward and apart from the roller 7 on the support member. For example, if the circumferential speed of one of the rollers 6, 7 varies, and the magnitude of shearing force Fs.6.7 changes, a vertical FN.6.7 generated by the initial load of an accumulator 29 and compression between the rollers 6, 7 are kept constant.