Speed reducer, production method for speed reducer, roller bearing, crankshaft and production method for crank shaft

A speed reducer comprising:

• a crankshaft adapted to be rotated in conjunction with a drive unit;
• a first eccentric portion provided on said crankshaft;
• a second eccentric portion provided on said crankshaft;
• a third eccentric portion provided on said crankshaft;
• a first externally-toothed gear adapted to be moved in conjunction with said first eccentric portion;
• a second externally-toothed gear adapted to be moved in conjunction with said second eccentric portion;
• a third externally-toothed gear adapted to be moved in conjunction with said third eccentric portion;
• a plurality of pin teeth disposed along an inner periphery of a case to allow each of said first, second and third externally-toothed gears to be in meshing engagement therewith;
• and
• an output shaft unit adapted to be rotated in conjunction with said first, second and third externally-toothed gears,
• wherein said first, second and third eccentric portions are arranged with a given phase difference in a rotation direction of said crankshaft with respect to each other,
• wherein each of said first, second and third externally-toothed gears is in meshing engagement with less than half of said plurality of pin teeth.