PURPOSE: To increase load capacity in the bearing of a gear shaft as well as to improve the extent of durability in the bearing, by letting a tooth space flow oil in this tooth space immediately after passing through a suction port back to the suction port side by way of the circumference of the gear shaft.

CONSTITUTION: Concave parts 16 and 17 are formed in a side plate facing the tooth space of tooth spaces G1 of gears 2 and 3 immediately after passing through a suction port 18, and these concaves parts 16 and 17 are interconnected to oil grooves 14 and 15 being formed in shaft holes 12 and 13 via annular grooves 19 and 20 formed in a boundary part between these gears 2, 3 and gear shafts 14 and 15. Since these oil grooves 14 and 15 are interconnected to the side of the suction port 18 via clearances 21 and 22 between the gear shaft and a mounting flange (m) and a notch part 23, if high pressure oil at the side of the tooth space G2 is penetrated into the tooth space G1, this pressure oil lubricates a bearing part in low pressure and then flows back to the suction port side.