Speed reduction or speed increasing apparatus

A speed reduction or speed increasing apparatus, comprising:

• a first crown gear fixed to a housing;
• a second crown gear fixed to an output portion and rotatable with respect to the housing;
• a third crown gear having opposing teeth facing the first crown gear and opposing teeth facing the second gear, back to back with respect to each other;
• and
• a cam unit configured to incline the third crown gear with respect to the first and second crown gears in such a manner that the third crown gear engages with the first crown gear and the third crown gear engages with the second crown gear, and to cause the third crown gear to undergo wave motion in such a manner that locations of contact move in a circumferential direction,
• wherein:
• the cam unit includes a first cam placed on the first crown gear side with respect to the third crown gear, and a second cam placed on the second crown gear side with respect to the third crown gear,
• the first cam and the second cam sandwich the third crown gear,
• a first rolling element is disposed between the first cam and the third crown gear in such a manner as to be capable of rolling motion,
• a second rolling element is disposed between the second cam and the third crown gear in such a manner as to be capable of rolling motion,
• the first and second cams are fixed to an input shaft so as not to be rotatable,
• the first cam is directly rotatably supported by a first bearing disposed between the first crown gear and the first cam, and
• the second cam is directly rotatably supported by a second bearing disposed between the second crown gear and the second cam.