PURPOSE: To determine the interval between the shafts of a shaft fixing device by engaging plural gears furnishing rollers formed on the shafts coaxially to the rotation axis of the gears by hitting the rollers each other, and securing the just enough back lashes of the gears.

CONSTITUTION: A roller 2 and a roller 5 are made in the same pitch circular diameter of the respective gears, and a gear 1 and a gear 4 are engaged each other, but the pitches of the axial centers 3a and 6a of a gearing shaft 3 and a gearing shaft 6 are determined by the total sum of the outer diameters of the rollers 2 and 5. In this case, the gears and the rollers are formed separately, and they are assembled on the same axis. When the quality of the shaft fixing device is different from that of the gears, the rollers are made of the quality same as the shaft fixing device, so that the difference of the thermal expansion coefficient between the gears and the shaft fixing device can be absorbed.