To provide a cyclo speed reducer wherein inside gears can be manufactured more inexpensive than manufactured with sintering or machining work.

The first inside gear 80 and the second inside gear 86 are molded from plate metal members with pressing work to eliminate facilities and manhours which are conventionally required when manufacturing the inside gears with sintering or machining work. Thus, they can be manufactured more inexpensive than manufactured with sintering and machining work.