The same number of grooves 20 through 27 are provided in end surfaces 19a and 19b of a roller 19. The grooves 20 through 27 have communicating portions 20a through 27a which communicate with an inner peripheral side of the roller 19 and sealed portions 20b, 20c, 20d, 20e, 20f through 27b, 27c, 27d, 27e and 27f each of whose cross-sectional area decreases. Accordingly, the cross-sectional area is decreased in direction in which a lubricating oil flows, and a plurality of oil pressures can thus be obtained. This results in a fixed clearance of roller 19.