PURPOSE: To reduce the size of a gear device by providing plural thrust collars on both side surfaces of one side helical gear, and making one of plural clearances for discharging lubricating oil supplied to a gear and the thrust collars smaller than the other thereof.

CONSTITUTION: In a high peripheral speed helical gear, lubricating oil supplied to the mesh portion is pushed aside along the tooth trace following the rotation, and discharged to the side of the mesh end. Clearances are provided between the helical gear 8 and thrust collars 9. One clearance L2 on the mesh end side is adapted to discharge the lubricating oil obtained by adding the lubricating oil supplied to the thrust collar 9 contact surface to the lubricating oil pushed aside along the tooth trace. The other clearance L1 on the mesh start side is good for discharging only the lubricating oil supplied to the thrust collars 9 and can be made smaller than the mesh end side clearance L2. Thus, the distances between the collars 9 and between bearings can be decreased so as to reduce the size of the whole device.