rating of the first bearing into which the first insertion portion of one of the plurality of crankshafts is inserted is greater than the basic radial load ratings of the first bearings into which the first insertion portions of the remaining crankshafts among the plurality of crankshafts are inserted. With this constitution, the eccentric orbiting type speed reducer of this invention can prevent the life of the first bearing for rotatably holding the crankshaft having the rotational driving force input from being shorter. Therefore, the rotational driving force may be input into one crankshaft alone among the plurality of crankshafts. Consequently, the eccentric orbiting type speed reducer can be manufactured at lower costs by preventing an increase in the number of parts. In the eccentric orbiting type speedby the internal tooth member, while keeping a coaxial relation with the internal tooth member, a second rotational member with a plurality of circular grooves formed inside, the plurality of circular grooves being opposed respectively to the plurality of circular grooves for the first rotational member, the second rotational member being carried rotatably by the internal tooth member, while keeping a coaxial relation with the internal tooth member, an external gear having the external teeth formed on the outer circumference, with a plurality of through holes formed inside, the external teeth meshing with the internal teeth of the internal tooth member, the external gear being carried between the first rotational member and the second rotational member, a plurality of crankshafts having the first insertion portions to be inserted